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 $224.28   10.694%   $248.2645   $248.26   $248.25   $248.30  
  Purchase #2 $129.48   3.443%   $133.938   $133.94   $133.95   $133.90  
  Purchase #3 $65.52   11.133%   $72.8143   $72.81   $72.80   $72.80  
  Purchase #4 $82.74   9.217%   $90.3661   $90.37   $90.35   $90.40  
  Purchase #5 $178.98   9.247%   $195.5303   $195.53   $195.55   $195.50  
  Purchase #6 $114.50   12.307%   $128.5915   $128.59   $128.60   $128.60  
  Purchase #7 $102.48   13.123%   $115.9285   $115.93   $115.95   $115.90  
  7 purchase totals = $897.98       $985.4332   $985.43   $985.45   $985.40