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	$240.57	3.464%	$248.9033	$248.90	$248.90	$248.90
Purchase #2	$170.62	11.586%	$190.388	$190.39	$190.40	$190.40
Purchase #3	$134.26	13.867%	$152.8778	$152.88	$152.90	$152.90
Purchase #4	$30.74	4.631%	$32.1636	$32.16	$32.15	$32.20
Purchase #5	$249.98	6.766%	$266.8936	$266.89	$266.90	$266.90
Purchase #6	$182.53	4.555%	$190.8442	$190.84	$190.85	$190.80
Purchase #7	$125.95	11.333%	$140.2239	$140.22	$140.20	$140.20
7 purchase totals =	$1,134.65		$1,222.2944	$1,222.28	$1,222.30	$1,222.30