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 $236.58   11.663%   $264.1723   $264.17   $264.15   $264.20  
  Purchase #2 $83.93   13.571%   $95.3201   $95.32   $95.30   $95.30  
  Purchase #3 $114.31   3.822%   $118.6789   $118.68   $118.70   $118.70  
  Purchase #4 $183.89   10.727%   $203.6159   $203.62   $203.60   $203.60  
  Purchase #5 $212.58   11.204%   $236.3975   $236.40   $236.40   $236.40  
  Purchase #6 $133.53   13.848%   $152.0212   $152.02   $152.00   $152.00  
  Purchase #7 $236.25   4.522%   $246.9332   $246.93   $246.95   $246.90  
  7 purchase totals = $1,201.07       $1,317.1391   $1,317.14   $1,317.10   $1,317.10