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	$244.67	11.801%	$273.5435	$273.54	$273.55	$273.50
Purchase #2	$143.35	9.408%	$156.8364	$156.84	$156.85	$156.80
Purchase #3	$146.89	12.382%	$165.0779	$165.08	$165.10	$165.10
Purchase #4	$65.60	10.755%	$72.6553	$72.66	$72.65	$72.70
Purchase #5	$55.29	7.102%	$59.2167	$59.22	$59.20	$59.20
Purchase #6	$237.42	3.223%	$245.072	$245.07	$245.05	$245.10
Purchase #7	$98.40	12.361%	$110.5632	$110.56	$110.55	$110.60
7 purchase totals =	$991.62		$1,082.9650	$1,082.97	$1,082.95	$1,083.00