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	$120.47	6.307%	$128.068	$128.07	$128.05	$128.10
Purchase #2	$185.70	5.378%	$195.6869	$195.69	$195.70	$195.70
Purchase #3	$245.95	9.196%	$268.5676	$268.57	$268.55	$268.60
Purchase #4	$78.54	4.316%	$81.9298	$81.93	$81.95	$81.90
Purchase #5	$191.50	11.813%	$214.1219	$214.12	$214.10	$214.10
Purchase #6	$94.88	6.136%	$100.7018	$100.70	$100.70	$100.70
Purchase #7	$93.80	7.173%	$100.5283	$100.53	$100.55	$100.50
7 purchase totals =	$1,010.84		$1,089.6043	$1,089.61	$1,089.60	$1,089.60