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 $32.96   6.693%   $35.166   $35.17   $35.15   $35.20  
  Purchase #2 $11.72   12.306%   $13.1623   $13.16   $13.15   $13.20  
  Purchase #3 $171.71   12.202%   $192.6621   $192.66   $192.65   $192.70  
  Purchase #4 $113.78   10.348%   $125.554   $125.55   $125.55   $125.60  
  Purchase #5 $236.66   3.438%   $244.7964   $244.80   $244.80   $244.80  
  Purchase #6 $11.94   3.809%   $12.3948   $12.39   $12.40   $12.40  
  Purchase #7 $118.88   6.442%   $126.5382   $126.54   $126.55   $126.50  
  7 purchase totals = $697.65       $750.2738   $750.27   $750.25   $750.40