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 $65.68   9.541%   $71.9465   $71.95   $71.95   $71.90  
  Purchase #2 $227.59   8.410%   $246.7303   $246.73   $246.75   $246.70  
  Purchase #3 $234.95   12.531%   $264.3916   $264.39   $264.40   $264.40  
  Purchase #4 $158.93   12.148%   $178.2368   $178.24   $178.25   $178.20  
  Purchase #5 $222.34   13.454%   $252.2536   $252.25   $252.25   $252.30  
  Purchase #6 $186.94   8.461%   $202.757   $202.76   $202.75   $202.80  
  Purchase #7 $71.69   6.777%   $76.5484   $76.55   $76.55   $76.50  
  7 purchase totals = $1,168.12       $1,292.8642   $1,292.87   $1,292.90   $1,292.80