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 $37.69   9.479%   $41.2626   $41.26   $41.25   $41.30  
  Purchase #2 $55.27   11.772%   $61.7764   $61.78   $61.80   $61.80  
  Purchase #3 $152.62   9.667%   $167.3738   $167.37   $167.35   $167.40  
  Purchase #4 $197.62   3.859%   $205.2462   $205.25   $205.25   $205.20  
  Purchase #5 $161.69   10.493%   $178.6561   $178.66   $178.65   $178.70  
  Purchase #6 $49.38   8.718%   $53.6849   $53.68   $53.70   $53.70  
  Purchase #7 $241.33   7.235%   $258.7902   $258.79   $258.80   $258.80  
  7 purchase totals = $895.60       $966.7902   $966.79   $966.80   $966.90