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 $233.84   3.623%   $242.312   $242.31   $242.30   $242.30  
  Purchase #2 $168.42   12.695%   $189.8009   $189.80   $189.80   $189.80  
  Purchase #3 $25.58   8.544%   $27.7656   $27.77   $27.75   $27.80  
  Purchase #4 $240.27   11.390%   $267.6368   $267.64   $267.65   $267.60  
  Purchase #5 $169.77   8.355%   $183.9543   $183.95   $183.95   $184.00  
  Purchase #6 $246.67   4.600%   $258.0168   $258.02   $258.00   $258.00  
  Purchase #7 $92.69   5.721%   $97.9928   $97.99   $98.00   $98.00  
  7 purchase totals = $1,177.24       $1,267.4792   $1,267.48   $1,267.45   $1,267.50