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	$79.29	7.519%	$85.2518	$85.25	$85.25	$85.30
Purchase #2	$132.55	10.862%	$146.9476	$146.95	$146.95	$146.90
Purchase #3	$182.98	4.552%	$191.3092	$191.31	$191.30	$191.30
Purchase #4	$53.61	5.419%	$56.5151	$56.52	$56.50	$56.50
Purchase #5	$90.69	3.767%	$94.1063	$94.11	$94.10	$94.10
Purchase #6	$212.86	7.603%	$229.0437	$229.04	$229.05	$229.00
Purchase #7	$127.88	12.262%	$143.5606	$143.56	$143.55	$143.60
7 purchase totals =	$879.86		$946.7343	$946.74	$946.70	$946.70