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 $242.52   4.733%   $253.9985   $254.00   $254.00   $254.00  
  Purchase #2 $202.70   13.860%   $230.7942   $230.79   $230.80   $230.80  
  Purchase #3 $14.82   11.605%   $16.5399   $16.54   $16.55   $16.50  
  Purchase #4 $93.76   9.163%   $102.3512   $102.35   $102.35   $102.40  
  Purchase #5 $95.57   6.705%   $101.978   $101.98   $102.00   $102.00  
  Purchase #6 $31.42   6.696%   $33.5239   $33.52   $33.50   $33.50  
  Purchase #7 $152.49   7.760%   $164.3232   $164.32   $164.30   $164.30  
  7 purchase totals = $833.28       $903.5089   $903.50   $903.50   $903.50