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 $49.93   6.843%   $53.3467   $53.35   $53.35   $53.30  
  Purchase #2 $54.99   11.330%   $61.2204   $61.22   $61.20   $61.20  
  Purchase #3 $208.26   6.183%   $221.1367   $221.14   $221.15   $221.10  
  Purchase #4 $52.49   13.635%   $59.647   $59.65   $59.65   $59.60  
  Purchase #5 $95.28   4.638%   $99.6991   $99.70   $99.70   $99.70  
  Purchase #6 $184.53   4.630%   $193.0737   $193.07   $193.05   $193.10  
  Purchase #7 $233.78   10.377%   $258.0394   $258.04   $258.05   $258.00  
  7 purchase totals = $879.26       $946.1630   $946.17   $946.15   $946.00