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	$147.56	4.123%	$153.6439	$153.64	$153.65	$153.60
Purchase #2	$150.87	13.224%	$170.821	$170.82	$170.80	$170.80
Purchase #3	$205.72	3.646%	$213.2206	$213.22	$213.20	$213.20
Purchase #4	$35.98	3.612%	$37.2796	$37.28	$37.30	$37.30
Purchase #5	$140.68	3.643%	$145.805	$145.81	$145.80	$145.80
Purchase #6	$54.40	6.503%	$57.9376	$57.94	$57.95	$57.90
Purchase #7	$128.46	11.222%	$142.8758	$142.88	$142.90	$142.90
7 purchase totals =	$863.67		$921.5835	$921.59	$921.60	$921.50