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	$18.71	6.493%	$19.9248	$19.92	$19.90	$19.90
Purchase #2	$145.95	3.507%	$151.0685	$151.07	$151.05	$151.10
Purchase #3	$112.52	13.783%	$128.0286	$128.03	$128.05	$128.00
Purchase #4	$230.34	7.865%	$248.4562	$248.46	$248.45	$248.50
Purchase #5	$94.63	11.816%	$105.8115	$105.81	$105.80	$105.80
Purchase #6	$59.84	7.222%	$64.1616	$64.16	$64.15	$64.20
Purchase #7	$199.46	12.457%	$224.3067	$224.31	$224.30	$224.30
7 purchase totals =	$861.45		$941.7579	$941.76	$941.70	$941.80