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 $67.51   11.256%   $75.1089   $75.11   $75.10   $75.10  
  Purchase #2 $222.55   11.574%   $248.3079   $248.31   $248.30   $248.30  
  Purchase #3 $135.49   10.843%   $150.1812   $150.18   $150.20   $150.20  
  Purchase #4 $40.64   10.418%   $44.8739   $44.87   $44.85   $44.90  
  Purchase #5 $213.37   10.644%   $236.0811   $236.08   $236.10   $236.10  
  Purchase #6 $196.91   11.703%   $219.9544   $219.95   $219.95   $220.00  
  Purchase #7 $139.98   8.110%   $151.3324   $151.33   $151.35   $151.30  
  7 purchase totals = $1,016.45       $1,125.8398   $1,125.83   $1,125.85   $1,125.90