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 $188.59   9.235%   $206.0063   $206.01   $206.00   $206.00  
  Purchase #2 $86.43   9.715%   $94.8267   $94.83   $94.85   $94.80  
  Purchase #3 $217.76   8.197%   $235.6098   $235.61   $235.60   $235.60  
  Purchase #4 $35.96   12.296%   $40.3816   $40.38   $40.40   $40.40  
  Purchase #5 $87.51   10.828%   $96.9856   $96.99   $97.00   $97.00  
  Purchase #6 $212.59   9.266%   $232.2886   $232.29   $232.30   $232.30  
  Purchase #7 $150.91   4.516%   $157.7251   $157.73   $157.75   $157.70  
  7 purchase totals = $979.75       $1,063.8237   $1,063.84   $1,063.90   $1,063.80