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 $82.79   6.827%   $88.4421   $88.44   $88.45   $88.40  
  Purchase #2 $168.89   8.798%   $183.7489   $183.75   $183.75   $183.70  
  Purchase #3 $8.32   10.553%   $9.198   $9.20   $9.20   $9.20  
  Purchase #4 $122.46   7.793%   $132.0033   $132.00   $132.00   $132.00  
  Purchase #5 $244.94   9.296%   $267.7096   $267.71   $267.70   $267.70  
  Purchase #6 $191.28   11.487%   $213.2523   $213.25   $213.25   $213.30  
  Purchase #7 $173.61   8.176%   $187.8044   $187.80   $187.80   $187.80  
  7 purchase totals = $992.29       $1,082.1586   $1,082.15   $1,082.15   $1,082.10