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 $186.86   4.250%   $194.8016   $194.80   $194.80   $194.80  
  Purchase #2 $237.25   6.743%   $253.2478   $253.25   $253.25   $253.20  
  Purchase #3 $160.73   12.483%   $180.7939   $180.79   $180.80   $180.80  
  Purchase #4 $23.78   8.248%   $25.7414   $25.74   $25.75   $25.70  
  Purchase #5 $187.33   12.503%   $210.7519   $210.75   $210.75   $210.80  
  Purchase #6 $44.59   3.827%   $46.2965   $46.30   $46.30   $46.30  
  Purchase #7 $30.26   5.256%   $31.8505   $31.85   $31.85   $31.90  
  7 purchase totals = $870.80       $943.4836   $943.48   $943.50   $943.50