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	$137.76	13.203%	$155.9485	$155.95	$155.95	$155.90
Purchase #2	$55.62	12.220%	$62.4168	$62.42	$62.40	$62.40
Purchase #3	$96.48	6.669%	$102.9143	$102.91	$102.90	$102.90
Purchase #4	$40.76	10.440%	$45.0153	$45.02	$45.00	$45.00
Purchase #5	$33.70	5.367%	$35.5087	$35.51	$35.50	$35.50
Purchase #6	$211.55	10.682%	$234.1478	$234.15	$234.15	$234.10
Purchase #7	$138.34	10.311%	$152.6042	$152.60	$152.60	$152.60
7 purchase totals =	$714.21		$788.5556	$788.56	$788.50	$788.40