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 $69.80   7.725%   $75.1921   $75.19   $75.20   $75.20  
  Purchase #2 $194.89   4.260%   $203.1923   $203.19   $203.20   $203.20  
  Purchase #3 $246.34   4.730%   $257.9919   $257.99   $258.00   $258.00  
  Purchase #4 $47.59   12.535%   $53.5554   $53.56   $53.55   $53.60  
  Purchase #5 $13.29   3.757%   $13.7893   $13.79   $13.80   $13.80  
  Purchase #6 $103.56   10.456%   $114.3882   $114.39   $114.40   $114.40  
  Purchase #7 $197.90   11.428%   $220.516   $220.52   $220.50   $220.50  
  7 purchase totals = $873.37       $938.6252   $938.63   $938.65   $938.70