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 $185.78   9.226%   $202.9201   $202.92   $202.90   $202.90  
  Purchase #2 $77.86   9.631%   $85.3587   $85.36   $85.35   $85.40  
  Purchase #3 $9.76   6.108%   $10.3561   $10.36   $10.35   $10.40  
  Purchase #4 $246.66   6.382%   $262.4018   $262.40   $262.40   $262.40  
  Purchase #5 $143.34   9.610%   $157.115   $157.12   $157.10   $157.10  
  Purchase #6 $58.99   10.540%   $65.2075   $65.21   $65.20   $65.20  
  Purchase #7 $198.84   6.765%   $212.2915   $212.29   $212.30   $212.30  
  7 purchase totals = $921.23       $995.6507   $995.66   $995.60   $995.70