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	$230.64	3.537%	$238.7977	$238.80	$238.80	$238.80
Purchase #2	$106.44	10.249%	$117.349	$117.35	$117.35	$117.30
Purchase #3	$247.30	12.590%	$278.4351	$278.44	$278.45	$278.40
Purchase #4	$71.71	7.516%	$77.0997	$77.10	$77.10	$77.10
Purchase #5	$33.36	7.339%	$35.8083	$35.81	$35.80	$35.80
Purchase #6	$84.98	4.812%	$89.0692	$89.07	$89.05	$89.10
Purchase #7	$38.40	11.617%	$42.8609	$42.86	$42.85	$42.90
7 purchase totals =	$812.83		$879.4199	$879.43	$879.40	$879.40