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 $142.32   6.573%   $151.6747   $151.67   $151.65   $151.70  
  Purchase #2 $198.62   13.612%   $225.6562   $225.66   $225.65   $225.70  
  Purchase #3 $111.48   4.353%   $116.3327   $116.33   $116.35   $116.30  
  Purchase #4 $249.52   11.530%   $278.2897   $278.29   $278.30   $278.30  
  Purchase #5 $226.49   9.238%   $247.4131   $247.41   $247.40   $247.40  
  Purchase #6 $235.72   12.243%   $264.5792   $264.58   $264.60   $264.60  
  Purchase #7 $130.26   8.441%   $141.2552   $141.26   $141.25   $141.30  
  7 purchase totals = $1,294.41       $1,425.2008   $1,425.20   $1,425.20   $1,425.30