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 $58.72   3.105%   $60.5433   $60.54   $60.55   $60.50  
  Purchase #2 $93.50   6.565%   $99.6383   $99.64   $99.65   $99.60  
  Purchase #3 $237.44   3.437%   $245.6008   $245.60   $245.60   $245.60  
  Purchase #4 $181.95   9.688%   $199.5773   $199.58   $199.60   $199.60  
  Purchase #5 $84.73   4.860%   $88.8479   $88.85   $88.85   $88.80  
  Purchase #6 $41.42   5.288%   $43.6103   $43.61   $43.60   $43.60  
  Purchase #7 $116.65   6.497%   $124.2288   $124.23   $124.25   $124.20  
  7 purchase totals = $814.41       $862.0467   $862.05   $862.10   $861.90