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	$25.98	4.588%	$27.172	$27.17	$27.15	$27.20
Purchase #2	$191.94	3.408%	$198.4813	$198.48	$198.50	$198.50
Purchase #3	$127.37	9.667%	$139.6829	$139.68	$139.70	$139.70
Purchase #4	$28.40	13.598%	$32.2618	$32.26	$32.25	$32.30
Purchase #5	$162.38	5.782%	$171.7688	$171.77	$171.75	$171.80
Purchase #6	$231.65	8.124%	$250.4692	$250.47	$250.45	$250.50
Purchase #7	$239.37	9.597%	$262.3423	$262.34	$262.35	$262.30
7 purchase totals =	$1,007.09		$1,082.1783	$1,082.17	$1,082.15	$1,082.30