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 $43.53   13.252%   $49.2986   $49.30   $49.30   $49.30  
  Purchase #2 $194.78   12.623%   $219.3671   $219.37   $219.35   $219.40  
  Purchase #3 $195.69   9.217%   $213.7267   $213.73   $213.75   $213.70  
  Purchase #4 $201.30   5.617%   $212.607   $212.61   $212.60   $212.60  
  Purchase #5 $187.33   5.450%   $197.5395   $197.54   $197.55   $197.50  
  Purchase #6 $50.67   8.775%   $55.1163   $55.12   $55.10   $55.10  
  Purchase #7 $25.62   9.288%   $27.9996   $28.00   $28.00   $28.00  
  7 purchase totals = $898.92       $975.6548   $975.67   $975.65   $975.60