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 $54.99   10.139%   $60.5654   $60.57   $60.55   $60.60  
  Purchase #2 $129.64   12.621%   $146.0019   $146.00   $146.00   $146.00  
  Purchase #3 $121.40   3.293%   $125.3977   $125.40   $125.40   $125.40  
  Purchase #4 $64.71   6.620%   $68.9938   $68.99   $69.00   $69.00  
  Purchase #5 $70.61   6.327%   $75.0775   $75.08   $75.10   $75.10  
  Purchase #6 $202.56   5.614%   $213.9317   $213.93   $213.95   $213.90  
  Purchase #7 $37.92   11.858%   $42.4166   $42.42   $42.40   $42.40  
  7 purchase totals = $681.83       $732.3846   $732.39   $732.40   $732.40