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	$76.64	11.559%	$85.4988	$85.50	$85.50	$85.50
Purchase #2	$202.40	3.321%	$209.1217	$209.12	$209.10	$209.10
Purchase #3	$139.92	4.148%	$145.7239	$145.72	$145.70	$145.70
Purchase #4	$95.66	9.636%	$104.8778	$104.88	$104.90	$104.90
Purchase #5	$115.92	9.610%	$127.0599	$127.06	$127.05	$127.10
Purchase #6	$7.92	10.746%	$8.7711	$8.77	$8.75	$8.80
Purchase #7	$125.27	13.761%	$142.5084	$142.51	$142.50	$142.50
7 purchase totals =	$763.73		$823.5616	$823.56	$823.50	$823.60