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 $37.81   13.282%   $42.8319   $42.83   $42.85   $42.80  
  Purchase #2 $243.96   9.154%   $266.2921   $266.29   $266.30   $266.30  
  Purchase #3 $64.29   4.388%   $67.111   $67.11   $67.10   $67.10  
  Purchase #4 $66.67   10.792%   $73.865   $73.87   $73.85   $73.90  
  Purchase #5 $191.72   10.302%   $211.471   $211.47   $211.45   $211.50  
  Purchase #6 $23.85   11.817%   $26.6684   $26.67   $26.65   $26.70  
  Purchase #7 $162.78   4.406%   $169.9521   $169.95   $169.95   $170.00  
  7 purchase totals = $791.08       $858.1915   $858.19   $858.15   $858.30