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	$90.30	11.371%	$100.568	$100.57	$100.55	$100.60
Purchase #2	$147.27	13.417%	$167.0292	$167.03	$167.05	$167.00
Purchase #3	$250.44	10.767%	$277.4049	$277.40	$277.40	$277.40
Purchase #4	$166.85	3.420%	$172.5563	$172.56	$172.55	$172.60
Purchase #5	$246.57	7.238%	$264.4167	$264.42	$264.40	$264.40
Purchase #6	$112.46	4.830%	$117.8918	$117.89	$117.90	$117.90
Purchase #7	$93.48	13.207%	$105.8259	$105.83	$105.85	$105.80
7 purchase totals =	$1,107.37		$1,205.6928	$1,205.70	$1,205.70	$1,205.70