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 $66.51   11.111%   $73.8999   $73.90   $73.90   $73.90  
  Purchase #2 $206.46   4.403%   $215.5504   $215.55   $215.55   $215.60  
  Purchase #3 $52.69   10.427%   $58.184   $58.18   $58.20   $58.20  
  Purchase #4 $36.71   12.161%   $41.1743   $41.17   $41.15   $41.20  
  Purchase #5 $142.44   5.611%   $150.4323   $150.43   $150.45   $150.40  
  Purchase #6 $115.34   12.800%   $130.1035   $130.10   $130.10   $130.10  
  Purchase #7 $237.90   10.735%   $263.4386   $263.44   $263.45   $263.40  
  7 purchase totals = $858.05       $932.7830   $932.77   $932.80   $932.80