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	$134.85	13.155%	$152.5895	$152.59	$152.60	$152.60
Purchase #2	$78.33	13.356%	$88.7918	$88.79	$88.80	$88.80
Purchase #3	$66.65	10.814%	$73.8575	$73.86	$73.85	$73.90
Purchase #4	$61.87	8.695%	$67.2496	$67.25	$67.25	$67.20
Purchase #5	$233.38	7.618%	$251.1589	$251.16	$251.15	$251.20
Purchase #6	$154.33	13.859%	$175.7186	$175.72	$175.70	$175.70
Purchase #7	$169.59	3.793%	$176.0225	$176.02	$176.00	$176.00
7 purchase totals =	$899.00		$985.3884	$985.39	$985.35	$985.40