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 $68.81   6.821%   $73.5035   $73.50   $73.50   $73.50  
  Purchase #2 $77.95   13.567%   $88.5255   $88.53   $88.55   $88.50  
  Purchase #3 $162.89   12.641%   $183.4809   $183.48   $183.50   $183.50  
  Purchase #4 $79.99   6.397%   $85.107   $85.11   $85.10   $85.10  
  Purchase #5 $57.44   13.479%   $65.1823   $65.18   $65.20   $65.20  
  Purchase #6 $14.37   11.472%   $16.0185   $16.02   $16.00   $16.00  
  Purchase #7 $203.36   13.787%   $231.3972   $231.40   $231.40   $231.40  
  7 purchase totals = $664.81       $743.2149   $743.22   $743.25   $743.20