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 $60.55   3.436%   $62.6305   $62.63   $62.65   $62.60  
  Purchase #2 $97.57   3.521%   $101.0054   $101.01   $101.00   $101.00  
  Purchase #3 $12.32   11.153%   $13.694   $13.69   $13.70   $13.70  
  Purchase #4 $16.84   6.630%   $17.9565   $17.96   $17.95   $18.00  
  Purchase #5 $154.91   3.586%   $160.4651   $160.47   $160.45   $160.50  
  Purchase #6 $99.58   13.440%   $112.9636   $112.96   $112.95   $113.00  
  Purchase #7 $109.94   9.405%   $120.2799   $120.28   $120.30   $120.30  
  7 purchase totals = $551.71       $588.9950   $589.00   $589.00   $589.10