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	$18.28	6.823%	$19.5272	$19.53	$19.55	$19.50
Purchase #2	$38.86	8.401%	$42.1246	$42.12	$42.10	$42.10
Purchase #3	$227.49	8.636%	$247.136	$247.14	$247.15	$247.10
Purchase #4	$168.25	11.592%	$187.7535	$187.75	$187.75	$187.80
Purchase #5	$162.72	4.358%	$169.8113	$169.81	$169.80	$169.80
Purchase #6	$124.72	5.300%	$131.3302	$131.33	$131.35	$131.30
Purchase #7	$65.46	12.486%	$73.6333	$73.63	$73.65	$73.60
7 purchase totals =	$805.78		$871.3161	$871.31	$871.35	$871.20