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	$137.96	4.598%	$144.3034	$144.30	$144.30	$144.30
Purchase #2	$99.29	10.600%	$109.8147	$109.81	$109.80	$109.80
Purchase #3	$198.97	11.595%	$222.0406	$222.04	$222.05	$222.00
Purchase #4	$30.56	5.718%	$32.3074	$32.31	$32.30	$32.30
Purchase #5	$208.27	8.270%	$225.4939	$225.49	$225.50	$225.50
Purchase #6	$182.54	5.213%	$192.0558	$192.06	$192.05	$192.10
Purchase #7	$41.87	11.506%	$46.6876	$46.69	$46.70	$46.70
7 purchase totals =	$899.46		$972.7034	$972.70	$972.70	$972.70