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 $61.49   3.849%   $63.8568   $63.86   $63.85   $63.90  
  Purchase #2 $247.71   4.581%   $259.0576   $259.06   $259.05   $259.10  
  Purchase #3 $169.54   9.489%   $185.6277   $185.63   $185.65   $185.60  
  Purchase #4 $27.28   6.501%   $29.0535   $29.05   $29.05   $29.10  
  Purchase #5 $175.39   13.814%   $199.6184   $199.62   $199.60   $199.60  
  Purchase #6 $86.38   9.454%   $94.5464   $94.55   $94.55   $94.50  
  Purchase #7 $225.73   7.503%   $242.6665   $242.67   $242.65   $242.70  
  7 purchase totals = $993.52       $1,074.4269   $1,074.44   $1,074.40   $1,074.50