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 $237.27   9.383%   $259.533   $259.53   $259.55   $259.50  
  Purchase #2 $218.28   12.545%   $245.6632   $245.66   $245.65   $245.70  
  Purchase #3 $120.27   10.847%   $133.3157   $133.32   $133.30   $133.30  
  Purchase #4 $65.49   6.117%   $69.496   $69.50   $69.50   $69.50  
  Purchase #5 $150.77   4.402%   $157.4069   $157.41   $157.40   $157.40  
  Purchase #6 $179.75   8.345%   $194.7501   $194.75   $194.75   $194.80  
  Purchase #7 $207.68   8.722%   $225.7938   $225.79   $225.80   $225.80  
  7 purchase totals = $1,179.51       $1,285.9587   $1,285.96   $1,285.95   $1,286.00