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 $183.68   6.532%   $195.678   $195.68   $195.70   $195.70  
  Purchase #2 $71.73   6.371%   $76.2999   $76.30   $76.30   $76.30  
  Purchase #3 $245.80   11.798%   $274.7995   $274.80   $274.80   $274.80  
  Purchase #4 $163.27   12.175%   $183.1481   $183.15   $183.15   $183.10  
  Purchase #5 $66.53   12.122%   $74.5948   $74.59   $74.60   $74.60  
  Purchase #6 $108.63   4.329%   $113.3326   $113.33   $113.35   $113.30  
  Purchase #7 $153.84   7.600%   $165.5318   $165.53   $165.55   $165.50  
  7 purchase totals = $993.48       $1,083.3847   $1,083.38   $1,083.45   $1,083.30