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 $115.30   6.846%   $123.1934   $123.19   $123.20   $123.20  
  Purchase #2 $235.95   11.296%   $262.6029   $262.60   $262.60   $262.60  
  Purchase #3 $9.75   7.441%   $10.4755   $10.48   $10.50   $10.50  
  Purchase #4 $121.43   9.257%   $132.6708   $132.67   $132.65   $132.70  
  Purchase #5 $100.49   6.554%   $107.0761   $107.08   $107.10   $107.10  
  Purchase #6 $150.36   13.566%   $170.7578   $170.76   $170.75   $170.80  
  Purchase #7 $131.70   13.475%   $149.4466   $149.45   $149.45   $149.40  
  7 purchase totals = $864.98       $956.2231   $956.23   $956.25   $956.30