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	$130.55	4.477%	$136.3947	$136.39	$136.40	$136.40
Purchase #2	$226.55	7.316%	$243.1244	$243.12	$243.10	$243.10
Purchase #3	$116.43	3.159%	$120.108	$120.11	$120.10	$120.10
Purchase #4	$192.83	4.172%	$200.8749	$200.87	$200.85	$200.90
Purchase #5	$209.61	10.318%	$231.2376	$231.24	$231.25	$231.20
Purchase #6	$127.27	12.865%	$143.6433	$143.64	$143.65	$143.60
Purchase #7	$196.28	4.167%	$204.459	$204.46	$204.45	$204.50
7 purchase totals =	$1,199.52		$1,279.8419	$1,279.83	$1,279.80	$1,279.80