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 $50.36   10.445%   $55.6201   $55.62   $55.60   $55.60  
  Purchase #2 $195.76   10.222%   $215.7706   $215.77   $215.75   $215.80  
  Purchase #3 $245.78   7.375%   $263.9063   $263.91   $263.90   $263.90  
  Purchase #4 $233.90   3.155%   $241.2795   $241.28   $241.30   $241.30  
  Purchase #5 $206.30   6.345%   $219.3897   $219.39   $219.40   $219.40  
  Purchase #6 $161.36   11.668%   $180.1875   $180.19   $180.20   $180.20  
  Purchase #7 $242.45   7.278%   $260.0955   $260.10   $260.10   $260.10  
  7 purchase totals = $1,335.91       $1,436.2492   $1,436.26   $1,436.25   $1,436.30