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 $43.90   11.783%   $49.0727   $49.07   $49.05   $49.10  
  Purchase #2 $239.68   9.765%   $263.0848   $263.08   $263.10   $263.10  
  Purchase #3 $248.37   8.254%   $268.8705   $268.87   $268.85   $268.90  
  Purchase #4 $58.37   5.717%   $61.707   $61.71   $61.70   $61.70  
  Purchase #5 $39.53   7.799%   $42.6129   $42.61   $42.60   $42.60  
  Purchase #6 $30.84   11.818%   $34.4847   $34.48   $34.50   $34.50  
  Purchase #7 $18.50   11.584%   $20.643   $20.64   $20.65   $20.60  
  7 purchase totals = $679.19       $740.4756   $740.46   $740.45   $740.50