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 $41.61   5.196%   $43.7721   $43.77   $43.75   $43.80  
  Purchase #2 $58.95   5.543%   $62.2176   $62.22   $62.20   $62.20  
  Purchase #3 $234.50   12.769%   $264.4433   $264.44   $264.45   $264.40  
  Purchase #4 $73.88   5.219%   $77.7358   $77.74   $77.75   $77.70  
  Purchase #5 $221.30   5.804%   $234.1443   $234.14   $234.15   $234.10  
  Purchase #6 $149.90   5.135%   $157.5974   $157.60   $157.60   $157.60  
  Purchase #7 $199.77   10.774%   $221.2932   $221.29   $221.30   $221.30  
  7 purchase totals = $979.91       $1,061.2037   $1,061.20   $1,061.20   $1,061.10