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 $30.97   6.782%   $33.0704   $33.07   $33.05   $33.10  
  Purchase #2 $211.43   7.531%   $227.3528   $227.35   $227.35   $227.40  
  Purchase #3 $103.57   9.645%   $113.5593   $113.56   $113.55   $113.60  
  Purchase #4 $221.68   6.251%   $235.5372   $235.54   $235.55   $235.50  
  Purchase #5 $67.80   11.733%   $75.755   $75.76   $75.75   $75.80  
  Purchase #6 $39.61   3.664%   $41.0613   $41.06   $41.05   $41.10  
  Purchase #7 $231.96   11.592%   $258.8488   $258.85   $258.85   $258.80  
  7 purchase totals = $907.02       $985.1848   $985.19   $985.15   $985.30