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	$244.27	4.600%	$255.5064	$255.51	$255.50	$255.50
Purchase #2	$156.74	4.813%	$164.2839	$164.28	$164.30	$164.30
Purchase #3	$161.66	6.628%	$172.3748	$172.37	$172.35	$172.40
Purchase #4	$37.27	7.725%	$40.1491	$40.15	$40.15	$40.10
Purchase #5	$188.26	3.829%	$195.4685	$195.47	$195.45	$195.50
Purchase #6	$121.52	11.802%	$135.8618	$135.86	$135.85	$135.90
Purchase #7	$27.62	9.119%	$30.1387	$30.14	$30.15	$30.10
7 purchase totals =	$937.34		$993.7832	$993.78	$993.75	$993.80