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	$164.92	3.175%	$170.1562	$170.16	$170.15	$170.20
Purchase #2	$140.74	6.817%	$150.3342	$150.33	$150.35	$150.30
Purchase #3	$218.41	5.377%	$230.1539	$230.15	$230.15	$230.20
Purchase #4	$64.56	5.168%	$67.8965	$67.90	$67.90	$67.90
Purchase #5	$25.28	7.573%	$27.1945	$27.19	$27.20	$27.20
Purchase #6	$158.83	7.764%	$171.1616	$171.16	$171.15	$171.20
Purchase #7	$105.95	10.288%	$116.8501	$116.85	$116.85	$116.90
7 purchase totals =	$878.69		$933.7470	$933.74	$933.75	$933.90