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 $85.73   12.757%   $96.6666   $96.67   $96.65   $96.70  
  Purchase #2 $29.76   3.864%   $30.9099   $30.91   $30.90   $30.90  
  Purchase #3 $223.73   11.270%   $248.9444   $248.94   $248.95   $248.90  
  Purchase #4 $95.63   9.294%   $104.5179   $104.52   $104.50   $104.50  
  Purchase #5 $107.36   13.554%   $121.9116   $121.91   $121.90   $121.90  
  Purchase #6 $85.93   9.425%   $94.0289   $94.03   $94.05   $94.00  
  Purchase #7 $59.64   12.458%   $67.07   $67.07   $67.05   $67.10  
  7 purchase totals = $687.78       $764.0493   $764.05   $764.00   $764.00