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 $204.84   9.327%   $223.9454   $223.95   $223.95   $223.90  
  Purchase #2 $176.73   8.829%   $192.3335   $192.33   $192.35   $192.30  
  Purchase #3 $75.69   7.110%   $81.0716   $81.07   $81.05   $81.10  
  Purchase #4 $95.71   4.714%   $100.2218   $100.22   $100.20   $100.20  
  Purchase #5 $55.44   5.771%   $58.6394   $58.64   $58.65   $58.60  
  Purchase #6 $174.76   6.369%   $185.8905   $185.89   $185.90   $185.90  
  Purchase #7 $154.46   9.821%   $169.6295   $169.63   $169.65   $169.60  
  7 purchase totals = $937.63       $1,011.7317   $1,011.73   $1,011.75   $1,011.60