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 $45.73   13.532%   $51.9182   $51.92   $51.90   $51.90  
  Purchase #2 $177.77   4.680%   $186.0896   $186.09   $186.10   $186.10  
  Purchase #3 $211.72   13.683%   $240.6896   $240.69   $240.70   $240.70  
  Purchase #4 $41.65   8.550%   $45.2111   $45.21   $45.20   $45.20  
  Purchase #5 $203.71   5.140%   $214.1807   $214.18   $214.20   $214.20  
  Purchase #6 $120.86   9.263%   $132.0553   $132.06   $132.05   $132.10  
  Purchase #7 $23.39   4.866%   $24.5282   $24.53   $24.55   $24.50  
  7 purchase totals = $824.83       $894.6727   $894.68   $894.70   $894.70