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 $60.86   9.674%   $66.7476   $66.75   $66.75   $66.70  
  Purchase #2 $75.45   3.316%   $77.9519   $77.95   $77.95   $78.00  
  Purchase #3 $164.50   11.234%   $182.9799   $182.98   $183.00   $183.00  
  Purchase #4 $229.26   12.218%   $257.271   $257.27   $257.25   $257.30  
  Purchase #5 $147.76   3.308%   $152.6479   $152.65   $152.65   $152.60  
  Purchase #6 $239.27   10.387%   $264.123   $264.12   $264.10   $264.10  
  Purchase #7 $12.85   3.277%   $13.2711   $13.27   $13.25   $13.30  
  7 purchase totals = $929.95       $1,014.9924   $1,014.99   $1,014.95   $1,015.00