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	$75.89	13.645%	$86.2452	$86.25	$86.25	$86.20
Purchase #2	$42.76	5.584%	$45.1477	$45.15	$45.15	$45.10
Purchase #3	$170.86	13.330%	$193.6356	$193.64	$193.65	$193.60
Purchase #4	$35.75	10.784%	$39.6053	$39.61	$39.60	$39.60
Purchase #5	$55.34	12.374%	$62.1878	$62.19	$62.20	$62.20
Purchase #6	$139.30	12.691%	$156.9786	$156.98	$157.00	$157.00
Purchase #7	$149.86	4.686%	$156.8824	$156.88	$156.90	$156.90
7 purchase totals =	$669.76		$740.6826	$740.70	$740.75	$740.60