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	$50.74	11.360%	$56.5041	$56.50	$56.50	$56.50
Purchase #2	$150.55	8.166%	$162.8439	$162.84	$162.85	$162.80
Purchase #3	$207.66	13.224%	$235.121	$235.12	$235.10	$235.10
Purchase #4	$213.36	13.227%	$241.5811	$241.58	$241.60	$241.60
Purchase #5	$209.82	6.530%	$223.5212	$223.52	$223.50	$223.50
Purchase #6	$167.96	9.290%	$183.5635	$183.56	$183.55	$183.60
Purchase #7	$42.48	7.487%	$45.6605	$45.66	$45.65	$45.70
7 purchase totals =	$1,042.57		$1,148.7953	$1,148.78	$1,148.75	$1,148.80