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	$20.86	3.170%	$21.5213	$21.52	$21.50	$21.50
Purchase #2	$73.59	7.186%	$78.8782	$78.88	$78.90	$78.90
Purchase #3	$168.86	13.607%	$191.8368	$191.84	$191.85	$191.80
Purchase #4	$19.65	5.497%	$20.7302	$20.73	$20.75	$20.70
Purchase #5	$112.97	4.498%	$118.0514	$118.05	$118.05	$118.10
Purchase #6	$153.67	7.640%	$165.4104	$165.41	$165.40	$165.40
Purchase #7	$200.74	10.129%	$221.073	$221.07	$221.05	$221.10
7 purchase totals =	$750.34		$817.5013	$817.50	$817.50	$817.50