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 $227.75   10.565%   $251.8118   $251.81   $251.80   $251.80  
  Purchase #2 $162.53   4.381%   $169.6504   $169.65   $169.65   $169.70  
  Purchase #3 $76.26   10.741%   $84.4511   $84.45   $84.45   $84.50  
  Purchase #4 $154.90   9.674%   $169.885   $169.89   $169.90   $169.90  
  Purchase #5 $9.82   13.296%   $11.1257   $11.13   $11.15   $11.10  
  Purchase #6 $211.81   3.631%   $219.5008   $219.50   $219.50   $219.50  
  Purchase #7 $120.34   13.169%   $136.1876   $136.19   $136.20   $136.20  
  7 purchase totals = $963.41       $1,042.6124   $1,042.62   $1,042.65   $1,042.70