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	$45.35	10.277%	$50.0106	$50.01	$50.00	$50.00
Purchase #2	$187.86	12.756%	$211.8234	$211.82	$211.80	$211.80
Purchase #3	$14.80	11.489%	$16.5004	$16.50	$16.50	$16.50
Purchase #4	$168.29	12.823%	$189.8698	$189.87	$189.85	$189.90
Purchase #5	$86.55	5.282%	$91.1216	$91.12	$91.10	$91.10
Purchase #6	$66.53	7.535%	$71.543	$71.54	$71.55	$71.50
Purchase #7	$52.62	13.388%	$59.6648	$59.66	$59.65	$59.70
7 purchase totals =	$622.00		$690.5336	$690.52	$690.45	$690.50