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 $155.48   4.318%   $162.1936   $162.19   $162.20   $162.20  
  Purchase #2 $57.47   3.684%   $59.5872   $59.59   $59.60   $59.60  
  Purchase #3 $39.26   12.577%   $44.1977   $44.20   $44.20   $44.20  
  Purchase #4 $60.50   12.173%   $67.8647   $67.86   $67.85   $67.90  
  Purchase #5 $163.80   13.547%   $185.99   $185.99   $186.00   $186.00  
  Purchase #6 $245.37   6.461%   $261.2234   $261.22   $261.20   $261.20  
  Purchase #7 $177.38   10.108%   $195.3096   $195.31   $195.30   $195.30  
  7 purchase totals = $899.26       $976.3662   $976.36   $976.35   $976.40