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 $244.87   12.379%   $275.1825   $275.18   $275.20   $275.20  
  Purchase #2 $22.58   11.457%   $25.167   $25.17   $25.15   $25.20  
  Purchase #3 $189.50   7.863%   $204.4004   $204.40   $204.40   $204.40  
  Purchase #4 $142.36   12.406%   $160.0212   $160.02   $160.00   $160.00  
  Purchase #5 $62.63   12.799%   $70.646   $70.65   $70.65   $70.60  
  Purchase #6 $224.65   12.162%   $251.9719   $251.97   $251.95   $252.00  
  Purchase #7 $246.59   12.127%   $276.494   $276.49   $276.50   $276.50  
  7 purchase totals = $1,133.18       $1,263.8830   $1,263.88   $1,263.85   $1,263.90