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	$140.55	11.345%	$156.4954	$156.50	$156.50	$156.50
Purchase #2	$73.30	12.498%	$82.461	$82.46	$82.45	$82.50
Purchase #3	$240.54	5.752%	$254.3759	$254.38	$254.40	$254.40
Purchase #4	$147.34	7.694%	$158.6763	$158.68	$158.70	$158.70
Purchase #5	$62.80	13.245%	$71.1179	$71.12	$71.10	$71.10
Purchase #6	$122.35	4.219%	$127.5119	$127.51	$127.50	$127.50
Purchase #7	$210.32	5.438%	$221.7572	$221.76	$221.75	$221.80
7 purchase totals =	$997.20		$1,072.3956	$1,072.41	$1,072.40	$1,072.50