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 $250.63   10.414%   $276.7306   $276.73   $276.75   $276.70  
  Purchase #2 $211.75   12.301%   $237.7974   $237.80   $237.80   $237.80  
  Purchase #3 $157.26   11.467%   $175.293   $175.29   $175.30   $175.30  
  Purchase #4 $239.57   9.346%   $261.9602   $261.96   $261.95   $262.00  
  Purchase #5 $203.85   12.771%   $229.8837   $229.88   $229.90   $229.90  
  Purchase #6 $8.55   13.316%   $9.6885   $9.69   $9.70   $9.70  
  Purchase #7 $133.77   11.304%   $148.8914   $148.89   $148.90   $148.90  
  7 purchase totals = $1,205.38       $1,340.2448   $1,340.24   $1,340.30   $1,340.30