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 $48.70   10.816%   $53.9674   $53.97   $53.95   $54.00  
  Purchase #2 $203.80   11.171%   $226.5665   $226.57   $226.55   $226.60  
  Purchase #3 $54.77   13.227%   $62.0144   $62.01   $62.00   $62.00  
  Purchase #4 $209.85   9.348%   $229.4668   $229.47   $229.45   $229.50  
  Purchase #5 $27.71   4.151%   $28.8602   $28.86   $28.85   $28.90  
  Purchase #6 $244.93   12.264%   $274.9682   $274.97   $274.95   $275.00  
  Purchase #7 $136.68   9.604%   $149.8067   $149.81   $149.80   $149.80  
  7 purchase totals = $926.44       $1,025.6502   $1,025.66   $1,025.55   $1,025.80