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 $53.77   12.533%   $60.509   $60.51   $60.50   $60.50  
  Purchase #2 $247.80   7.174%   $265.5772   $265.58   $265.60   $265.60  
  Purchase #3 $221.79   10.793%   $245.7278   $245.73   $245.75   $245.70  
  Purchase #4 $92.99   5.855%   $98.4346   $98.43   $98.45   $98.40  
  Purchase #5 $177.85   6.777%   $189.9029   $189.90   $189.90   $189.90  
  Purchase #6 $107.86   4.516%   $112.731   $112.73   $112.75   $112.70  
  Purchase #7 $68.51   10.418%   $75.6474   $75.65   $75.65   $75.60  
  7 purchase totals = $970.57       $1,048.5299   $1,048.53   $1,048.60   $1,048.40