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	$73.71	12.871%	$83.1972	$83.20	$83.20	$83.20
Purchase #2	$123.73	4.681%	$129.5218	$129.52	$129.50	$129.50
Purchase #3	$114.61	11.132%	$127.3684	$127.37	$127.35	$127.40
Purchase #4	$212.29	13.125%	$240.1531	$240.15	$240.15	$240.20
Purchase #5	$175.25	9.775%	$192.3807	$192.38	$192.40	$192.40
Purchase #6	$156.72	12.640%	$176.5294	$176.53	$176.55	$176.50
Purchase #7	$165.91	11.781%	$185.4559	$185.46	$185.45	$185.50
7 purchase totals =	$1,022.22		$1,134.6065	$1,134.61	$1,134.60	$1,134.70