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 $148.74   10.473%   $164.3175   $164.32   $164.30   $164.30  
  Purchase #2 $202.71   5.656%   $214.1753   $214.18   $214.20   $214.20  
  Purchase #3 $125.39   8.580%   $136.1485   $136.15   $136.15   $136.10  
  Purchase #4 $112.94   9.147%   $123.2706   $123.27   $123.25   $123.30  
  Purchase #5 $142.52   11.200%   $158.4822   $158.48   $158.50   $158.50  
  Purchase #6 $182.42   13.783%   $207.5629   $207.56   $207.55   $207.60  
  Purchase #7 $45.75   12.111%   $51.2908   $51.29   $51.30   $51.30  
  7 purchase totals = $960.47       $1,055.2478   $1,055.25   $1,055.25   $1,055.30