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 $84.34   5.208%   $88.7324   $88.73   $88.75   $88.70  
  Purchase #2 $119.49   5.591%   $126.1707   $126.17   $126.15   $126.20  
  Purchase #3 $237.98   5.572%   $251.2402   $251.24   $251.25   $251.20  
  Purchase #4 $230.53   4.655%   $241.2612   $241.26   $241.25   $241.30  
  Purchase #5 $225.65   8.121%   $243.975   $243.98   $244.00   $244.00  
  Purchase #6 $197.43   11.662%   $220.4543   $220.45   $220.45   $220.50  
  Purchase #7 $129.91   11.528%   $144.886   $144.89   $144.90   $144.90  
  7 purchase totals = $1,225.33       $1,316.7198   $1,316.72   $1,316.75   $1,316.80