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	$223.66	6.560%	$238.3321	$238.33	$238.35	$238.30
Purchase #2	$149.98	6.528%	$159.7707	$159.77	$159.75	$159.80
Purchase #3	$131.52	4.204%	$137.0491	$137.05	$137.05	$137.00
Purchase #4	$100.42	10.629%	$111.0936	$111.09	$111.10	$111.10
Purchase #5	$119.55	10.674%	$132.3108	$132.31	$132.30	$132.30
Purchase #6	$144.53	4.227%	$150.6393	$150.64	$150.65	$150.60
Purchase #7	$42.74	4.823%	$44.8014	$44.80	$44.80	$44.80
7 purchase totals =	$912.40		$973.9970	$973.99	$974.00	$973.90