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 $161.33   13.271%   $182.7401   $182.74   $182.75   $182.70  
  Purchase #2 $200.34   9.589%   $219.5506   $219.55   $219.55   $219.60  
  Purchase #3 $54.76   5.460%   $57.7499   $57.75   $57.75   $57.70  
  Purchase #4 $81.53   8.833%   $88.7315   $88.73   $88.75   $88.70  
  Purchase #5 $112.51   3.362%   $116.2926   $116.29   $116.30   $116.30  
  Purchase #6 $177.61   13.678%   $201.9035   $201.90   $201.90   $201.90  
  Purchase #7 $182.71   12.649%   $205.821   $205.82   $205.80   $205.80  
  7 purchase totals = $970.79       $1,072.7892   $1,072.78   $1,072.80   $1,072.70