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 $235.56   6.872%   $251.7477   $251.75   $251.75   $251.70  
  Purchase #2 $5.27   13.322%   $5.9721   $5.97   $5.95   $6.00  
  Purchase #3 $169.79   3.821%   $176.2777   $176.28   $176.30   $176.30  
  Purchase #4 $72.51   9.247%   $79.215   $79.22   $79.20   $79.20  
  Purchase #5 $222.56   4.113%   $231.7139   $231.71   $231.70   $231.70  
  Purchase #6 $242.47   7.353%   $260.2988   $260.30   $260.30   $260.30  
  Purchase #7 $116.66   4.417%   $121.8129   $121.81   $121.80   $121.80  
  7 purchase totals = $1,064.82       $1,127.0381   $1,127.04   $1,127.00   $1,127.00