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	$37.39	12.580%	$42.0937	$42.09	$42.10	$42.10
Purchase #2	$16.62	11.721%	$18.568	$18.57	$18.55	$18.60
Purchase #3	$62.33	8.679%	$67.7396	$67.74	$67.75	$67.70
Purchase #4	$165.41	12.185%	$185.5652	$185.57	$185.55	$185.60
Purchase #5	$187.90	3.860%	$195.1529	$195.15	$195.15	$195.20
Purchase #6	$67.31	11.125%	$74.7982	$74.80	$74.80	$74.80
Purchase #7	$134.42	4.808%	$140.8829	$140.88	$140.90	$140.90
7 purchase totals =	$671.38		$724.8005	$724.80	$724.80	$724.90