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	$243.70	4.154%	$253.8233	$253.82	$253.80	$253.80
Purchase #2	$150.97	11.869%	$168.8886	$168.89	$168.90	$168.90
Purchase #3	$222.88	5.828%	$235.8694	$235.87	$235.85	$235.90
Purchase #4	$99.31	4.504%	$103.7829	$103.78	$103.80	$103.80
Purchase #5	$40.25	12.355%	$45.2229	$45.22	$45.20	$45.20
Purchase #6	$52.81	3.379%	$54.5944	$54.59	$54.60	$54.60
Purchase #7	$50.94	7.198%	$54.6067	$54.61	$54.60	$54.60
7 purchase totals =	$860.86		$916.7882	$916.78	$916.75	$916.80