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 $36.64   13.131%   $41.4512   $41.45   $41.45   $41.50  
  Purchase #2 $198.92   3.223%   $205.3312   $205.33   $205.35   $205.30  
  Purchase #3 $19.75   11.453%   $22.012   $22.01   $22.00   $22.00  
  Purchase #4 $27.40   3.455%   $28.3467   $28.35   $28.35   $28.30  
  Purchase #5 $159.98   4.702%   $167.5023   $167.50   $167.50   $167.50  
  Purchase #6 $60.54   11.383%   $67.4313   $67.43   $67.45   $67.40  
  Purchase #7 $21.28   11.233%   $23.6704   $23.67   $23.65   $23.70  
  7 purchase totals = $524.51       $555.7451   $555.74   $555.75   $555.70