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 $201.58   12.698%   $227.1766   $227.18   $227.20   $227.20  
  Purchase #2 $5.28   12.419%   $5.9357   $5.94   $5.95   $5.90  
  Purchase #3 $41.46   9.712%   $45.4866   $45.49   $45.50   $45.50  
  Purchase #4 $65.89   4.280%   $68.7101   $68.71   $68.70   $68.70  
  Purchase #5 $153.37   4.713%   $160.5983   $160.60   $160.60   $160.60  
  Purchase #6 $236.52   3.743%   $245.3729   $245.37   $245.35   $245.40  
  Purchase #7 $11.81   7.480%   $12.6934   $12.69   $12.70   $12.70  
  7 purchase totals = $715.91       $765.9736   $765.98   $766.00   $766.00