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	$57.77	4.630%	$60.4448	$60.44	$60.45	$60.40
Purchase #2	$191.34	12.404%	$215.0738	$215.07	$215.05	$215.10
Purchase #3	$11.46	10.111%	$12.6187	$12.62	$12.60	$12.60
Purchase #4	$56.70	5.273%	$59.6898	$59.69	$59.70	$59.70
Purchase #5	$243.63	11.198%	$270.9117	$270.91	$270.90	$270.90
Purchase #6	$69.68	5.355%	$73.4114	$73.41	$73.40	$73.40
Purchase #7	$137.32	6.242%	$145.8915	$145.89	$145.90	$145.90
7 purchase totals =	$767.90		$838.0417	$838.03	$838.00	$838.00