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	$48.51	9.618%	$53.1757	$53.18	$53.20	$53.20
Purchase #2	$203.43	9.289%	$222.3266	$222.33	$222.35	$222.30
Purchase #3	$222.52	7.536%	$239.2891	$239.29	$239.30	$239.30
Purchase #4	$209.57	5.455%	$221.002	$221.00	$221.00	$221.00
Purchase #5	$142.30	3.263%	$146.9432	$146.94	$146.95	$146.90
Purchase #6	$31.57	12.204%	$35.4228	$35.42	$35.40	$35.40
Purchase #7	$195.37	13.865%	$222.4581	$222.46	$222.45	$222.50
7 purchase totals =	$1,053.27		$1,140.6175	$1,140.62	$1,140.65	$1,140.60