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 $125.52   8.830%   $136.6034   $136.60   $136.60   $136.60  
  Purchase #2 $152.35   6.565%   $162.3518   $162.35   $162.35   $162.40  
  Purchase #3 $212.90   13.256%   $241.122   $241.12   $241.10   $241.10  
  Purchase #4 $199.82   12.771%   $225.339   $225.34   $225.35   $225.30  
  Purchase #5 $16.42   13.554%   $18.6456   $18.65   $18.65   $18.60  
  Purchase #6 $190.25   12.755%   $214.5164   $214.52   $214.50   $214.50  
  Purchase #7 $183.68   5.238%   $193.3012   $193.30   $193.30   $193.30  
  7 purchase totals = $1,080.94       $1,191.8794   $1,191.88   $1,191.85   $1,191.80