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 $165.86   5.702%   $175.3173   $175.32   $175.30   $175.30  
  Purchase #2 $178.71   9.120%   $195.0084   $195.01   $195.00   $195.00  
  Purchase #3 $249.46   3.406%   $257.9566   $257.96   $257.95   $258.00  
  Purchase #4 $95.68   3.184%   $98.7265   $98.73   $98.75   $98.70  
  Purchase #5 $50.45   9.604%   $55.2952   $55.30   $55.30   $55.30  
  Purchase #6 $206.43   9.612%   $226.2721   $226.27   $226.25   $226.30  
  Purchase #7 $179.33   3.643%   $185.863   $185.86   $185.85   $185.90  
  7 purchase totals = $1,125.92       $1,194.4391   $1,194.45   $1,194.40   $1,194.50