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	$73.35	13.661%	$83.3703	$83.37	$83.35	$83.40
Purchase #2	$174.78	6.107%	$185.4538	$185.45	$185.45	$185.50
Purchase #3	$119.73	8.514%	$129.9238	$129.92	$129.90	$129.90
Purchase #4	$11.59	5.763%	$12.2579	$12.26	$12.25	$12.30
Purchase #5	$174.38	9.465%	$190.8851	$190.89	$190.90	$190.90
Purchase #6	$57.33	13.323%	$64.9681	$64.97	$64.95	$65.00
Purchase #7	$244.76	8.151%	$264.7104	$264.71	$264.70	$264.70
7 purchase totals =	$855.92		$931.5694	$931.57	$931.50	$931.70