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	$144.38	7.644%	$155.4164	$155.42	$155.40	$155.40
Purchase #2	$228.48	9.310%	$249.7515	$249.75	$249.75	$249.80
Purchase #3	$109.71	11.451%	$122.2729	$122.27	$122.25	$122.30
Purchase #4	$66.77	6.445%	$71.0733	$71.07	$71.05	$71.10
Purchase #5	$100.27	11.515%	$111.8161	$111.82	$111.80	$111.80
Purchase #6	$73.57	12.107%	$82.4771	$82.48	$82.50	$82.50
Purchase #7	$88.68	7.865%	$95.6547	$95.65	$95.65	$95.70
7 purchase totals =	$811.86		$888.4620	$888.46	$888.40	$888.60