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	$50.61	9.418%	$55.3764	$55.38	$55.40	$55.40
Purchase #2	$7.25	6.829%	$7.7451	$7.75	$7.75	$7.70
Purchase #3	$232.39	5.330%	$244.7764	$244.78	$244.80	$244.80
Purchase #4	$72.53	5.134%	$76.2537	$76.25	$76.25	$76.30
Purchase #5	$125.79	3.726%	$130.4769	$130.48	$130.50	$130.50
Purchase #6	$82.51	9.404%	$90.2692	$90.27	$90.25	$90.30
Purchase #7	$41.27	3.451%	$42.6942	$42.69	$42.70	$42.70
7 purchase totals =	$612.35		$647.5919	$647.60	$647.65	$647.70