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   9.705%   $60.3268   $60.33   $60.35   $60.30  
  Purchase #2 $146.45   13.677%   $166.48   $166.48   $166.50   $166.50  
  Purchase #3 $16.46   10.779%   $18.2342   $18.23   $18.25   $18.20  
  Purchase #4 $234.69   8.649%   $254.9883   $254.99   $255.00   $255.00  
  Purchase #5 $134.68   10.853%   $149.2968   $149.30   $149.30   $149.30  
  Purchase #6 $193.41   3.411%   $200.0072   $200.01   $200.00   $200.00  
  Purchase #7 $88.71   4.449%   $92.6567   $92.66   $92.65   $92.70  
  7 purchase totals = $869.39       $941.9900   $942.00   $942.05   $942.00