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 $35.81   11.760%   $40.0213   $40.02   $40.00   $40.00  
  Purchase #2 $168.64   5.716%   $178.2795   $178.28   $178.30   $178.30  
  Purchase #3 $157.42   5.270%   $165.716   $165.72   $165.70   $165.70  
  Purchase #4 $19.75   11.574%   $22.0359   $22.04   $22.05   $22.00  
  Purchase #5 $166.67   13.289%   $188.8188   $188.82   $188.80   $188.80  
  Purchase #6 $175.46   12.594%   $197.5574   $197.56   $197.55   $197.60  
  Purchase #7 $230.25   11.485%   $256.6942   $256.69   $256.70   $256.70  
  7 purchase totals = $954.00       $1,049.1231   $1,049.13   $1,049.10   $1,049.10