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 $48.47   8.458%   $52.5696   $52.57   $52.55   $52.60  
  Purchase #2 $29.81   13.494%   $33.8326   $33.83   $33.85   $33.80  
  Purchase #3 $157.67   11.859%   $176.3681   $176.37   $176.35   $176.40  
  Purchase #4 $194.45   11.265%   $216.3548   $216.35   $216.35   $216.40  
  Purchase #5 $34.73   5.656%   $36.6943   $36.69   $36.70   $36.70  
  Purchase #6 $169.93   11.764%   $189.9206   $189.92   $189.90   $189.90  
  Purchase #7 $41.94   11.421%   $46.73   $46.73   $46.75   $46.70  
  7 purchase totals = $677.00       $752.4700   $752.46   $752.45   $752.50