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 $212.93   13.297%   $241.2433   $241.24   $241.25   $241.20  
  Purchase #2 $97.50   7.709%   $105.0163   $105.02   $105.00   $105.00  
  Purchase #3 $109.67   6.277%   $116.554   $116.55   $116.55   $116.60  
  Purchase #4 $31.87   9.738%   $34.9735   $34.97   $34.95   $35.00  
  Purchase #5 $130.72   5.304%   $137.6534   $137.65   $137.65   $137.70  
  Purchase #6 $92.86   6.426%   $98.8272   $98.83   $98.85   $98.80  
  Purchase #7 $177.67   7.478%   $190.9562   $190.96   $190.95   $191.00  
  7 purchase totals = $853.22       $925.2239   $925.22   $925.20   $925.30