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	$7.67	8.344%	$8.31	$8.31	$8.30	$8.30
Purchase #2	$200.90	11.318%	$223.6379	$223.64	$223.65	$223.60
Purchase #3	$145.53	9.869%	$159.8924	$159.89	$159.90	$159.90
Purchase #4	$143.92	10.867%	$159.5598	$159.56	$159.55	$159.60
Purchase #5	$24.50	4.412%	$25.5809	$25.58	$25.60	$25.60
Purchase #6	$99.48	9.768%	$109.1972	$109.20	$109.20	$109.20
Purchase #7	$150.27	8.152%	$162.52	$162.52	$162.50	$162.50
7 purchase totals =	$772.27		$848.6982	$848.70	$848.70	$848.70