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 $241.29   9.507%   $264.2294   $264.23   $264.25   $264.20  
  Purchase #2 $250.38   7.419%   $268.9557   $268.96   $268.95   $269.00  
  Purchase #3 $98.63   11.559%   $110.0306   $110.03   $110.05   $110.00  
  Purchase #4 $218.94   12.216%   $245.6857   $245.69   $245.70   $245.70  
  Purchase #5 $76.97   7.296%   $82.5857   $82.59   $82.60   $82.60  
  Purchase #6 $11.51   7.195%   $12.3381   $12.34   $12.35   $12.30  
  Purchase #7 $120.93   10.807%   $133.9989   $134.00   $134.00   $134.00  
  7 purchase totals = $1,018.65       $1,117.8241   $1,117.84   $1,117.90   $1,117.80