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 $232.58   13.824%   $264.7319   $264.73   $264.75   $264.70  
  Purchase #2 $76.86   9.225%   $83.9503   $83.95   $83.95   $84.00  
  Purchase #3 $24.54   11.286%   $27.3096   $27.31   $27.30   $27.30  
  Purchase #4 $159.93   7.639%   $172.1471   $172.15   $172.15   $172.10  
  Purchase #5 $66.83   10.853%   $74.0831   $74.08   $74.10   $74.10  
  Purchase #6 $237.67   5.805%   $251.4667   $251.47   $251.45   $251.50  
  Purchase #7 $144.81   9.622%   $158.7436   $158.74   $158.75   $158.70  
  7 purchase totals = $943.22       $1,032.4323   $1,032.43   $1,032.45   $1,032.40