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	$172.88	6.861%	$184.7413	$184.74	$184.75	$184.70
Purchase #2	$115.79	13.808%	$131.7783	$131.78	$131.80	$131.80
Purchase #3	$216.80	3.144%	$223.6162	$223.62	$223.60	$223.60
Purchase #4	$46.50	8.358%	$50.3865	$50.39	$50.40	$50.40
Purchase #5	$210.46	13.257%	$238.3607	$238.36	$238.35	$238.40
Purchase #6	$60.54	10.511%	$66.9034	$66.90	$66.90	$66.90
Purchase #7	$232.58	7.179%	$249.2769	$249.28	$249.30	$249.30
7 purchase totals =	$1,055.55		$1,145.0633	$1,145.07	$1,145.10	$1,145.10