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	$139.62	4.226%	$145.5203	$145.52	$145.50	$145.50
Purchase #2	$205.28	4.323%	$214.1543	$214.15	$214.15	$214.20
Purchase #3	$140.36	3.822%	$145.7246	$145.72	$145.70	$145.70
Purchase #4	$175.25	12.217%	$196.6603	$196.66	$196.65	$196.70
Purchase #5	$6.37	10.839%	$7.0604	$7.06	$7.05	$7.10
Purchase #6	$142.79	4.280%	$148.9014	$148.90	$148.90	$148.90
Purchase #7	$116.67	3.332%	$120.5574	$120.56	$120.55	$120.60
7 purchase totals =	$926.34		$978.5787	$978.57	$978.50	$978.70