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 $56.27   13.145%   $63.6667   $63.67   $63.65   $63.70  
  Purchase #2 $27.40   7.718%   $29.5147   $29.51   $29.50   $29.50  
  Purchase #3 $237.70   10.118%   $261.7505   $261.75   $261.75   $261.80  
  Purchase #4 $33.42   13.604%   $37.9665   $37.97   $37.95   $38.00  
  Purchase #5 $56.53   10.579%   $62.5103   $62.51   $62.50   $62.50  
  Purchase #6 $101.43   6.651%   $108.1761   $108.18   $108.20   $108.20  
  Purchase #7 $211.46   3.485%   $218.8294   $218.83   $218.85   $218.80  
  7 purchase totals = $724.21       $782.4142   $782.42   $782.40   $782.50