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	$62.61	13.223%	$70.8889	$70.89	$70.90	$70.90
Purchase #2	$89.91	11.574%	$100.3162	$100.32	$100.30	$100.30
Purchase #3	$172.78	10.729%	$191.3176	$191.32	$191.30	$191.30
Purchase #4	$207.54	7.300%	$222.6904	$222.69	$222.70	$222.70
Purchase #5	$179.48	6.453%	$191.0618	$191.06	$191.05	$191.10
Purchase #6	$171.92	11.589%	$191.8438	$191.84	$191.85	$191.80
Purchase #7	$45.93	9.780%	$50.422	$50.42	$50.40	$50.40
7 purchase totals =	$930.17		$1,018.5407	$1,018.54	$1,018.50	$1,018.50