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 $246.83   5.241%   $259.7664   $259.77   $259.75   $259.80  
  Purchase #2 $198.99   3.540%   $206.0342   $206.03   $206.05   $206.00  
  Purchase #3 $201.72   8.653%   $219.1748   $219.17   $219.15   $219.20  
  Purchase #4 $32.85   10.177%   $36.1931   $36.19   $36.20   $36.20  
  Purchase #5 $7.60   11.434%   $8.469   $8.47   $8.45   $8.50  
  Purchase #6 $60.68   11.407%   $67.6018   $67.60   $67.60   $67.60  
  Purchase #7 $46.78   7.821%   $50.4387   $50.44   $50.45   $50.40  
  7 purchase totals = $795.45       $847.6780   $847.67   $847.65   $847.70