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	$10.32	4.710%	$10.8061	$10.81	$10.80	$10.80
Purchase #2	$124.81	4.390%	$130.2892	$130.29	$130.30	$130.30
Purchase #3	$151.37	3.800%	$157.1221	$157.12	$157.10	$157.10
Purchase #4	$81.73	12.691%	$92.1024	$92.10	$92.10	$92.10
Purchase #5	$222.78	6.107%	$236.3852	$236.39	$236.40	$236.40
Purchase #6	$92.29	13.516%	$104.7639	$104.76	$104.75	$104.80
Purchase #7	$82.66	9.388%	$90.4201	$90.42	$90.40	$90.40
7 purchase totals =	$765.96		$821.8890	$821.89	$821.85	$821.90