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	$101.57	8.678%	$110.3842	$110.38	$110.40	$110.40
Purchase #2	$219.67	10.474%	$242.6782	$242.68	$242.70	$242.70
Purchase #3	$50.50	5.203%	$53.1275	$53.13	$53.15	$53.10
Purchase #4	$30.71	9.384%	$33.5918	$33.59	$33.60	$33.60
Purchase #5	$62.53	6.499%	$66.5938	$66.59	$66.60	$66.60
Purchase #6	$37.64	10.753%	$41.6874	$41.69	$41.70	$41.70
Purchase #7	$97.25	3.762%	$100.9085	$100.91	$100.90	$100.90
7 purchase totals =	$599.87		$648.9714	$648.97	$649.05	$649.00