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	$222.37	8.239%	$240.6911	$240.69	$240.70	$240.70
Purchase #2	$119.78	3.143%	$123.5447	$123.54	$123.55	$123.50
Purchase #3	$72.45	8.443%	$78.567	$78.57	$78.55	$78.60
Purchase #4	$172.47	8.120%	$186.4746	$186.47	$186.45	$186.50
Purchase #5	$63.60	9.128%	$69.4054	$69.41	$69.40	$69.40
Purchase #6	$139.82	7.270%	$149.9849	$149.98	$150.00	$150.00
Purchase #7	$160.35	7.233%	$171.9481	$171.95	$171.95	$171.90
7 purchase totals =	$950.84		$1,020.6158	$1,020.61	$1,020.60	$1,020.60