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 $61.98   3.248%   $63.9931   $63.99   $64.00   $64.00  
  Purchase #2 $95.35   3.145%   $98.3488   $98.35   $98.35   $98.30  
  Purchase #3 $125.68   7.395%   $134.974   $134.97   $134.95   $135.00  
  Purchase #4 $184.62   8.188%   $199.7367   $199.74   $199.75   $199.70  
  Purchase #5 $185.28   3.765%   $192.2558   $192.26   $192.25   $192.30  
  Purchase #6 $70.58   7.768%   $76.0627   $76.06   $76.05   $76.10  
  Purchase #7 $246.49   13.543%   $279.8721   $279.87   $279.85   $279.90  
  7 purchase totals = $969.98       $1,045.2432   $1,045.24   $1,045.20   $1,045.30