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	$16.85	9.829%	$18.5062	$18.51	$18.50	$18.50
Purchase #2	$57.83	12.197%	$64.8835	$64.88	$64.90	$64.90
Purchase #3	$139.84	9.301%	$152.8465	$152.85	$152.85	$152.80
Purchase #4	$58.44	7.428%	$62.7809	$62.78	$62.80	$62.80
Purchase #5	$18.67	11.493%	$20.8157	$20.82	$20.80	$20.80
Purchase #6	$223.51	3.565%	$231.4781	$231.48	$231.50	$231.50
Purchase #7	$151.63	6.181%	$161.0023	$161.00	$161.00	$161.00
7 purchase totals =	$666.77		$712.3132	$712.32	$712.35	$712.30