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 $119.88   4.591%   $125.3837   $125.38   $125.40   $125.40  
  Purchase #2 $24.28   3.375%   $25.0995   $25.10   $25.10   $25.10  
  Purchase #3 $165.29   12.642%   $186.186   $186.19   $186.20   $186.20  
  Purchase #4 $17.52   4.245%   $18.2637   $18.26   $18.25   $18.30  
  Purchase #5 $224.51   9.588%   $246.036   $246.04   $246.05   $246.00  
  Purchase #6 $48.38   13.766%   $55.04   $55.04   $55.05   $55.00  
  Purchase #7 $212.98   5.107%   $223.8569   $223.86   $223.85   $223.90  
  7 purchase totals = $812.84       $879.8658   $879.87   $879.90   $879.90