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	$18.88	8.403%	$20.4665	$20.47	$20.45	$20.50
Purchase #2	$20.49	13.544%	$23.2652	$23.27	$23.25	$23.30
Purchase #3	$188.59	11.470%	$210.2213	$210.22	$210.20	$210.20
Purchase #4	$195.73	13.534%	$222.2201	$222.22	$222.20	$222.20
Purchase #5	$67.46	10.127%	$74.2917	$74.29	$74.30	$74.30
Purchase #6	$225.27	10.291%	$248.4525	$248.45	$248.45	$248.50
Purchase #7	$53.73	11.561%	$59.9417	$59.94	$59.95	$59.90
7 purchase totals =	$770.15		$858.8590	$858.86	$858.80	$858.90