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 $40.58   9.821%   $44.5654   $44.57   $44.55   $44.60  
  Purchase #2 $181.31   11.400%   $201.9793   $201.98   $202.00   $202.00  
  Purchase #3 $21.86   4.205%   $22.7792   $22.78   $22.80   $22.80  
  Purchase #4 $209.46   8.641%   $227.5594   $227.56   $227.55   $227.60  
  Purchase #5 $117.61   11.874%   $131.575   $131.58   $131.60   $131.60  
  Purchase #6 $164.84   8.742%   $179.2503   $179.25   $179.25   $179.30  
  Purchase #7 $24.26   8.843%   $26.4053   $26.41   $26.40   $26.40  
  7 purchase totals = $759.92       $834.1139   $834.13   $834.15   $834.30