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 $59.49   10.821%   $65.9274   $65.93   $65.95   $65.90  
  Purchase #2 $28.72   7.683%   $30.9266   $30.93   $30.95   $30.90  
  Purchase #3 $67.56   5.603%   $71.3454   $71.35   $71.35   $71.30  
  Purchase #4 $186.62   9.342%   $204.054   $204.05   $204.05   $204.10  
  Purchase #5 $56.96   4.637%   $59.6012   $59.60   $59.60   $59.60  
  Purchase #6 $128.32   4.315%   $133.857   $133.86   $133.85   $133.90  
  Purchase #7 $126.76   5.125%   $133.2565   $133.26   $133.25   $133.30  
  7 purchase totals = $654.43       $698.9681   $698.98   $699.00   $699.00