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 $23.43   7.452%   $25.176   $25.18   $25.20   $25.20  
  Purchase #2 $5.27   11.654%   $5.8842   $5.88   $5.90   $5.90  
  Purchase #3 $58.91   6.704%   $62.8593   $62.86   $62.85   $62.90  
  Purchase #4 $51.36   6.725%   $54.814   $54.81   $54.80   $54.80  
  Purchase #5 $233.97   5.508%   $246.8571   $246.86   $246.85   $246.90  
  Purchase #6 $235.71   10.295%   $259.9763   $259.98   $260.00   $260.00  
  Purchase #7 $132.62   5.731%   $140.2205   $140.22   $140.20   $140.20  
  7 purchase totals = $741.27       $795.7874   $795.79   $795.80   $795.90