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 $87.46   5.495%   $92.2659   $92.27   $92.25   $92.30  
  Purchase #2 $183.66   10.187%   $202.3694   $202.37   $202.35   $202.40  
  Purchase #3 $88.48   4.643%   $92.5881   $92.59   $92.60   $92.60  
  Purchase #4 $9.86   9.615%   $10.808   $10.81   $10.80   $10.80  
  Purchase #5 $225.48   13.388%   $255.6673   $255.67   $255.65   $255.70  
  Purchase #6 $207.80   11.857%   $232.4388   $232.44   $232.45   $232.40  
  Purchase #7 $84.46   10.855%   $93.6281   $93.63   $93.65   $93.60  
  7 purchase totals = $887.20       $979.7656   $979.78   $979.75   $979.80