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	$179.54	7.370%	$192.7721	$192.77	$192.75	$192.80
Purchase #2	$215.74	12.390%	$242.4702	$242.47	$242.45	$242.50
Purchase #3	$245.75	10.267%	$270.9812	$270.98	$271.00	$271.00
Purchase #4	$92.52	13.827%	$105.3127	$105.31	$105.30	$105.30
Purchase #5	$18.53	9.413%	$20.2742	$20.27	$20.25	$20.30
Purchase #6	$85.78	3.242%	$88.561	$88.56	$88.55	$88.60
Purchase #7	$72.57	10.195%	$79.9685	$79.97	$79.95	$80.00
7 purchase totals =	$910.43		$1,000.3399	$1,000.33	$1,000.25	$1,000.50