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 $60.25   7.394%   $64.7049   $64.70   $64.70   $64.70  
  Purchase #2 $225.56   9.662%   $247.3536   $247.35   $247.35   $247.40  
  Purchase #3 $27.82   12.648%   $31.3387   $31.34   $31.35   $31.30  
  Purchase #4 $155.82   4.775%   $163.2604   $163.26   $163.25   $163.30  
  Purchase #5 $240.46   8.773%   $261.5556   $261.56   $261.55   $261.60  
  Purchase #6 $98.57   7.496%   $105.9588   $105.96   $105.95   $106.00  
  Purchase #7 $25.58   13.177%   $28.9507   $28.95   $28.95   $29.00  
  7 purchase totals = $834.06       $903.1227   $903.12   $903.10   $903.30