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 $231.61   11.808%   $258.9585   $258.96   $258.95   $259.00  
  Purchase #2 $206.51   13.257%   $233.887   $233.89   $233.90   $233.90  
  Purchase #3 $69.82   13.484%   $79.2345   $79.23   $79.25   $79.20  
  Purchase #4 $246.27   10.142%   $271.2467   $271.25   $271.25   $271.20  
  Purchase #5 $45.34   12.416%   $50.9694   $50.97   $50.95   $51.00  
  Purchase #6 $81.56   10.158%   $89.8449   $89.84   $89.85   $89.80  
  Purchase #7 $58.87   3.104%   $60.6973   $60.70   $60.70   $60.70  
  7 purchase totals = $939.98       $1,044.8383   $1,044.84   $1,044.85   $1,044.80