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 $49.58   5.516%   $52.3148   $52.31   $52.30   $52.30  
  Purchase #2 $187.78   4.296%   $195.847   $195.85   $195.85   $195.80  
  Purchase #3 $126.70   13.873%   $144.2771   $144.28   $144.30   $144.30  
  Purchase #4 $69.80   4.831%   $73.172   $73.17   $73.15   $73.20  
  Purchase #5 $230.58   11.165%   $256.3243   $256.32   $256.30   $256.30  
  Purchase #6 $50.56   11.859%   $56.5559   $56.56   $56.55   $56.60  
  Purchase #7 $151.53   11.564%   $169.0529   $169.05   $169.05   $169.10  
  7 purchase totals = $866.53       $947.5440   $947.54   $947.50   $947.60