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 $217.83   6.654%   $232.3244   $232.32   $232.30   $232.30  
  Purchase #2 $125.93   5.624%   $133.0123   $133.01   $133.00   $133.00  
  Purchase #3 $9.67   7.210%   $10.3672   $10.37   $10.35   $10.40  
  Purchase #4 $225.95   13.595%   $256.6679   $256.67   $256.65   $256.70  
  Purchase #5 $63.31   5.193%   $66.5977   $66.60   $66.60   $66.60  
  Purchase #6 $109.39   12.744%   $123.3307   $123.33   $123.35   $123.30  
  Purchase #7 $180.31   13.513%   $204.6753   $204.68   $204.70   $204.70  
  7 purchase totals = $932.39       $1,026.9755   $1,026.98   $1,026.95   $1,027.00