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	$91.46	10.127%	$100.7222	$100.72	$100.70	$100.70
Purchase #2	$71.37	11.820%	$79.8059	$79.81	$79.80	$79.80
Purchase #3	$5.94	7.502%	$6.3856	$6.39	$6.40	$6.40
Purchase #4	$218.71	9.686%	$239.8943	$239.89	$239.90	$239.90
Purchase #5	$158.33	4.571%	$165.5673	$165.57	$165.55	$165.60
Purchase #6	$14.25	9.807%	$15.6475	$15.65	$15.65	$15.60
Purchase #7	$49.89	9.290%	$54.5248	$54.52	$54.50	$54.50
7 purchase totals =	$609.95		$662.5476	$662.55	$662.50	$662.50