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	$189.37	10.453%	$209.1648	$209.16	$209.15	$209.20
Purchase #2	$19.63	6.437%	$20.8936	$20.89	$20.90	$20.90
Purchase #3	$48.32	7.426%	$51.9082	$51.91	$51.90	$51.90
Purchase #4	$71.61	10.200%	$78.9142	$78.91	$78.90	$78.90
Purchase #5	$32.87	4.545%	$34.3639	$34.36	$34.35	$34.40
Purchase #6	$33.77	3.156%	$34.8358	$34.84	$34.85	$34.80
Purchase #7	$89.89	3.750%	$93.2609	$93.26	$93.25	$93.30
7 purchase totals =	$485.46		$523.3414	$523.33	$523.30	$523.40