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	$150.41	5.406%	$158.5412	$158.54	$158.55	$158.50
Purchase #2	$234.77	12.629%	$264.4191	$264.42	$264.40	$264.40
Purchase #3	$172.43	4.119%	$179.5324	$179.53	$179.55	$179.50
Purchase #4	$219.61	5.292%	$231.2318	$231.23	$231.25	$231.20
Purchase #5	$246.45	6.489%	$262.4421	$262.44	$262.45	$262.40
Purchase #6	$58.78	10.799%	$65.1277	$65.13	$65.15	$65.10
Purchase #7	$133.31	5.195%	$140.2355	$140.24	$140.25	$140.20
7 purchase totals =	$1,215.76		$1,301.5298	$1,301.53	$1,301.60	$1,301.30