Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $217.29   13.356%   $246.3113   $246.31   $246.30   $246.30  
  Purchase #2 $93.30   10.114%   $102.7364   $102.74   $102.75   $102.70  
  Purchase #3 $183.28   6.163%   $194.5755   $194.58   $194.60   $194.60  
  Purchase #4 $160.52   11.278%   $178.6234   $178.62   $178.60   $178.60  
  Purchase #5 $240.87   4.713%   $252.2222   $252.22   $252.20   $252.20  
  Purchase #6 $224.29   12.139%   $251.5166   $251.52   $251.50   $251.50  
  Purchase #7 $151.62   11.275%   $168.7152   $168.72   $168.70   $168.70  
  7 purchase totals = $1,271.17       $1,394.7006   $1,394.71   $1,394.65   $1,394.60