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 $200.61   8.338%   $217.3369   $217.34   $217.35   $217.30  
  Purchase #2 $193.88   11.582%   $216.3352   $216.34   $216.35   $216.30  
  Purchase #3 $69.26   12.222%   $77.725   $77.73   $77.75   $77.70  
  Purchase #4 $119.59   6.348%   $127.1816   $127.18   $127.20   $127.20  
  Purchase #5 $99.96   10.638%   $110.5937   $110.59   $110.60   $110.60  
  Purchase #6 $32.45   11.720%   $36.2531   $36.25   $36.25   $36.30  
  Purchase #7 $207.66   3.581%   $215.0963   $215.10   $215.10   $215.10  
  7 purchase totals = $923.41       $1,000.5218   $1,000.53   $1,000.60   $1,000.50