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	$75.82	3.457%	$78.4411	$78.44	$78.45	$78.40
Purchase #2	$28.58	7.859%	$30.8261	$30.83	$30.85	$30.80
Purchase #3	$141.76	6.789%	$151.3841	$151.38	$151.40	$151.40
Purchase #4	$37.97	10.364%	$41.9052	$41.91	$41.90	$41.90
Purchase #5	$217.92	9.590%	$238.8185	$238.82	$238.80	$238.80
Purchase #6	$17.57	6.246%	$18.6674	$18.67	$18.65	$18.70
Purchase #7	$42.75	7.207%	$45.831	$45.83	$45.85	$45.80
7 purchase totals =	$562.37		$605.8734	$605.88	$605.90	$605.80