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 $91.67   13.174%   $103.7466   $103.75   $103.75   $103.70  
  Purchase #2 $209.90   8.733%   $228.2306   $228.23   $228.25   $228.20  
  Purchase #3 $168.74   8.764%   $183.5284   $183.53   $183.55   $183.50  
  Purchase #4 $166.69   13.688%   $189.5065   $189.51   $189.50   $189.50  
  Purchase #5 $46.65   6.724%   $49.7867   $49.79   $49.80   $49.80  
  Purchase #6 $240.96   6.401%   $256.3838   $256.38   $256.40   $256.40  
  Purchase #7 $11.57   4.760%   $12.1207   $12.12   $12.10   $12.10  
  7 purchase totals = $936.18       $1,023.3033   $1,023.31   $1,023.35   $1,023.20