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 $246.98   5.639%   $260.9072   $260.91   $260.90   $260.90  
  Purchase #2 $124.93   6.664%   $133.2553   $133.26   $133.25   $133.30  
  Purchase #3 $179.77   12.784%   $202.7518   $202.75   $202.75   $202.80  
  Purchase #4 $168.75   6.543%   $179.7913   $179.79   $179.80   $179.80  
  Purchase #5 $224.61   7.504%   $241.4647   $241.46   $241.45   $241.50  
  Purchase #6 $148.82   12.641%   $167.6323   $167.63   $167.65   $167.60  
  Purchase #7 $111.63   6.728%   $119.1405   $119.14   $119.15   $119.10  
  7 purchase totals = $1,205.49       $1,304.9431   $1,304.94   $1,304.95   $1,305.00