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	$27.67	5.737%	$29.2574	$29.26	$29.25	$29.30
Purchase #2	$33.83	9.682%	$37.1054	$37.11	$37.10	$37.10
Purchase #3	$140.89	5.633%	$148.8263	$148.83	$148.85	$148.80
Purchase #4	$137.25	9.222%	$149.9072	$149.91	$149.90	$149.90
Purchase #5	$137.30	5.380%	$144.6867	$144.69	$144.70	$144.70
Purchase #6	$176.93	13.468%	$200.7589	$200.76	$200.75	$200.80
Purchase #7	$110.85	8.170%	$119.9064	$119.91	$119.90	$119.90
7 purchase totals =	$764.72		$830.4483	$830.47	$830.45	$830.50