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 $227.49   8.674%   $247.2225   $247.22   $247.20   $247.20  
  Purchase #2 $68.79   13.763%   $78.2576   $78.26   $78.25   $78.30  
  Purchase #3 $223.46   10.437%   $246.7825   $246.78   $246.80   $246.80  
  Purchase #4 $236.33   4.612%   $247.2295   $247.23   $247.25   $247.20  
  Purchase #5 $40.51   12.720%   $45.6629   $45.66   $45.65   $45.70  
  Purchase #6 $50.48   8.426%   $54.7334   $54.73   $54.75   $54.70  
  Purchase #7 $216.71   12.697%   $244.2257   $244.23   $244.25   $244.20  
  7 purchase totals = $1,063.77       $1,164.1141   $1,164.11   $1,164.15   $1,164.10