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	$229.84	3.816%	$238.6107	$238.61	$238.60	$238.60
Purchase #2	$160.25	12.658%	$180.5344	$180.53	$180.55	$180.50
Purchase #3	$124.34	9.757%	$136.4719	$136.47	$136.45	$136.50
Purchase #4	$159.47	9.428%	$174.5048	$174.50	$174.50	$174.50
Purchase #5	$93.27	6.819%	$99.6301	$99.63	$99.65	$99.60
Purchase #6	$153.75	10.252%	$169.5125	$169.51	$169.50	$169.50
Purchase #7	$190.80	12.261%	$214.194	$214.19	$214.20	$214.20
7 purchase totals =	$1,111.72		$1,213.4584	$1,213.44	$1,213.45	$1,213.40