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 $96.74   5.803%   $102.3538   $102.35   $102.35   $102.40  
  Purchase #2 $151.71   12.625%   $170.8634   $170.86   $170.85   $170.90  
  Purchase #3 $25.65   9.804%   $28.1647   $28.16   $28.15   $28.20  
  Purchase #4 $200.45   12.620%   $225.7468   $225.75   $225.75   $225.70  
  Purchase #5 $46.99   11.218%   $52.2613   $52.26   $52.25   $52.30  
  Purchase #6 $191.75   12.747%   $216.1924   $216.19   $216.20   $216.20  
  Purchase #7 $141.47   12.512%   $159.1707   $159.17   $159.15   $159.20  
  7 purchase totals = $854.76       $954.7531   $954.74   $954.70   $954.90