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 $56.60   11.287%   $62.9884   $62.99   $63.00   $63.00  
  Purchase #2 $244.38   4.466%   $255.294   $255.29   $255.30   $255.30  
  Purchase #3 $191.94   7.292%   $205.9363   $205.94   $205.95   $205.90  
  Purchase #4 $138.75   9.515%   $151.9521   $151.95   $151.95   $152.00  
  Purchase #5 $72.35   5.464%   $76.3032   $76.30   $76.30   $76.30  
  Purchase #6 $45.74   10.850%   $50.7028   $50.70   $50.70   $50.70  
  Purchase #7 $149.87   9.670%   $164.3624   $164.36   $164.35   $164.40  
  7 purchase totals = $899.63       $967.5392   $967.53   $967.55   $967.60