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 $214.47   6.291%   $227.9623   $227.96   $227.95   $228.00  
  Purchase #2 $10.56   5.392%   $11.1294   $11.13   $11.15   $11.10  
  Purchase #3 $248.77   6.190%   $264.1689   $264.17   $264.15   $264.20  
  Purchase #4 $70.55   8.526%   $76.5651   $76.57   $76.55   $76.60  
  Purchase #5 $106.36   3.667%   $110.2602   $110.26   $110.25   $110.30  
  Purchase #6 $169.44   3.550%   $175.4551   $175.46   $175.45   $175.50  
  Purchase #7 $17.42   4.730%   $18.244   $18.24   $18.25   $18.20  
  7 purchase totals = $837.57       $883.7850   $883.79   $883.75   $883.90