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 $186.57   11.707%   $208.4117   $208.41   $208.40   $208.40  
  Purchase #2 $27.38   8.112%   $29.6011   $29.60   $29.60   $29.60  
  Purchase #3 $53.48   12.435%   $60.1302   $60.13   $60.15   $60.10  
  Purchase #4 $230.59   5.113%   $242.3801   $242.38   $242.40   $242.40  
  Purchase #5 $208.72   11.509%   $232.7416   $232.74   $232.75   $232.70  
  Purchase #6 $118.77   11.168%   $132.0342   $132.03   $132.05   $132.00  
  Purchase #7 $56.92   8.337%   $61.6654   $61.67   $61.65   $61.70  
  7 purchase totals = $882.43       $966.9643   $966.96   $967.00   $966.90