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 $114.62   10.692%   $126.8752   $126.88   $126.90   $126.90  
  Purchase #2 $95.96   7.209%   $102.8778   $102.88   $102.90   $102.90  
  Purchase #3 $147.85   13.198%   $167.3632   $167.36   $167.35   $167.40  
  Purchase #4 $94.65   10.154%   $104.2608   $104.26   $104.25   $104.30  
  Purchase #5 $68.67   8.781%   $74.6999   $74.70   $74.70   $74.70  
  Purchase #6 $65.65   11.587%   $73.2569   $73.26   $73.25   $73.30  
  Purchase #7 $124.97   5.645%   $132.0246   $132.02   $132.00   $132.00  
  7 purchase totals = $712.37       $781.3584   $781.36   $781.35   $781.50