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 $202.38   11.428%   $225.508   $225.51   $225.50   $225.50  
  Purchase #2 $219.69   11.688%   $245.3674   $245.37   $245.35   $245.40  
  Purchase #3 $99.95   4.147%   $104.0949   $104.09   $104.10   $104.10  
  Purchase #4 $23.85   12.827%   $26.9092   $26.91   $26.90   $26.90  
  Purchase #5 $64.33   6.356%   $68.4188   $68.42   $68.40   $68.40  
  Purchase #6 $114.54   3.385%   $118.4172   $118.42   $118.40   $118.40  
  Purchase #7 $160.45   9.738%   $176.0746   $176.07   $176.05   $176.10  
  7 purchase totals = $885.19       $964.7901   $964.79   $964.70   $964.80