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 $172.47   3.541%   $178.5772   $178.58   $178.60   $178.60  
  Purchase #2 $108.50   9.248%   $118.5341   $118.53   $118.55   $118.50  
  Purchase #3 $123.75   7.383%   $132.8865   $132.89   $132.90   $132.90  
  Purchase #4 $97.88   7.367%   $105.0908   $105.09   $105.10   $105.10  
  Purchase #5 $28.96   4.102%   $30.1479   $30.15   $30.15   $30.10  
  Purchase #6 $17.85   9.549%   $19.5545   $19.55   $19.55   $19.60  
  Purchase #7 $49.55   5.139%   $52.0964   $52.10   $52.10   $52.10  
  7 purchase totals = $598.96       $636.8874   $636.89   $636.95   $636.90