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	$221.68	3.421%	$229.2637	$229.26	$229.25	$229.30
Purchase #2	$40.36	6.480%	$42.9753	$42.98	$43.00	$43.00
Purchase #3	$82.45	8.661%	$89.591	$89.59	$89.60	$89.60
Purchase #4	$134.72	10.479%	$148.8373	$148.84	$148.85	$148.80
Purchase #5	$89.91	7.450%	$96.6083	$96.61	$96.60	$96.60
Purchase #6	$14.29	3.246%	$14.7539	$14.75	$14.75	$14.80
Purchase #7	$51.57	11.648%	$57.5769	$57.58	$57.60	$57.60
7 purchase totals =	$634.98		$679.6064	$679.61	$679.65	$679.70