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 $209.99   7.781%   $226.3293   $226.33   $226.35   $226.30  
  Purchase #2 $54.99   13.231%   $62.2657   $62.27   $62.25   $62.30  
  Purchase #3 $41.83   5.468%   $44.1173   $44.12   $44.10   $44.10  
  Purchase #4 $172.27   4.663%   $180.303   $180.30   $180.30   $180.30  
  Purchase #5 $214.47   7.613%   $230.7976   $230.80   $230.80   $230.80  
  Purchase #6 $172.70   3.298%   $178.3956   $178.40   $178.40   $178.40  
  Purchase #7 $92.74   9.385%   $101.4436   $101.44   $101.45   $101.40  
  7 purchase totals = $958.99       $1,023.6521   $1,023.66   $1,023.65   $1,023.60