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 $168.53   13.833%   $191.8428   $191.84   $191.85   $191.80  
  Purchase #2 $21.90   9.239%   $23.9233   $23.92   $23.90   $23.90  
  Purchase #3 $155.55   8.421%   $168.6489   $168.65   $168.65   $168.60  
  Purchase #4 $51.59   4.277%   $53.7965   $53.80   $53.80   $53.80  
  Purchase #5 $250.62   8.795%   $272.662   $272.66   $272.65   $272.70  
  Purchase #6 $102.73   7.812%   $110.7553   $110.76   $110.75   $110.80  
  Purchase #7 $197.32   3.549%   $204.3229   $204.32   $204.30   $204.30  
  7 purchase totals = $948.24       $1,025.9517   $1,025.95   $1,025.90   $1,025.90