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 $86.44   9.842%   $94.9474   $94.95   $94.95   $94.90  
  Purchase #2 $183.40   6.417%   $195.1688   $195.17   $195.15   $195.20  
  Purchase #3 $185.39   9.772%   $203.5063   $203.51   $203.50   $203.50  
  Purchase #4 $18.90   7.189%   $20.2587   $20.26   $20.25   $20.30  
  Purchase #5 $62.38   8.819%   $67.8813   $67.88   $67.90   $67.90  
  Purchase #6 $88.45   6.107%   $93.8516   $93.85   $93.85   $93.90  
  Purchase #7 $116.85   9.787%   $128.2861   $128.29   $128.30   $128.30  
  7 purchase totals = $741.81       $803.9002   $803.91   $803.90   $804.00