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 $23.33   5.267%   $24.5588   $24.56   $24.55   $24.60  
  Purchase #2 $150.36   10.588%   $166.2801   $166.28   $166.30   $166.30  
  Purchase #3 $127.26   4.552%   $133.0529   $133.05   $133.05   $133.10  
  Purchase #4 $100.55   4.545%   $105.12   $105.12   $105.10   $105.10  
  Purchase #5 $70.84   9.720%   $77.7256   $77.73   $77.75   $77.70  
  Purchase #6 $181.69   9.251%   $198.4981   $198.50   $198.50   $198.50  
  Purchase #7 $50.84   4.266%   $53.0088   $53.01   $53.00   $53.00  
  7 purchase totals = $704.87       $758.2443   $758.25   $758.25   $758.30