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	$58.41	3.614%	$60.5209	$60.52	$60.50	$60.50
Purchase #2	$70.61	9.754%	$77.4973	$77.50	$77.50	$77.50
Purchase #3	$138.55	12.745%	$156.2082	$156.21	$156.20	$156.20
Purchase #4	$90.77	6.534%	$96.7009	$96.70	$96.70	$96.70
Purchase #5	$51.82	7.851%	$55.8884	$55.89	$55.90	$55.90
Purchase #6	$143.53	5.283%	$151.1127	$151.11	$151.10	$151.10
Purchase #7	$145.28	7.305%	$155.8927	$155.89	$155.90	$155.90
7 purchase totals =	$698.97		$753.8211	$753.82	$753.80	$753.80