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 $67.49   8.533%   $73.2489   $73.25   $73.25   $73.20  
  Purchase #2 $191.69   5.484%   $202.2023   $202.20   $202.20   $202.20  
  Purchase #3 $136.28   5.337%   $143.5533   $143.55   $143.55   $143.60  
  Purchase #4 $179.74   6.418%   $191.2757   $191.28   $191.30   $191.30  
  Purchase #5 $126.60   7.735%   $136.3925   $136.39   $136.40   $136.40  
  Purchase #6 $112.32   4.127%   $116.9554   $116.96   $116.95   $117.00  
  Purchase #7 $216.49   3.715%   $224.5326   $224.53   $224.55   $224.50  
  7 purchase totals = $1,030.61       $1,088.1607   $1,088.16   $1,088.20   $1,088.20