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	$224.46	12.681%	$252.9238	$252.92	$252.90	$252.90
Purchase #2	$18.86	8.614%	$20.4846	$20.48	$20.50	$20.50
Purchase #3	$91.50	11.585%	$102.1003	$102.10	$102.10	$102.10
Purchase #4	$28.71	8.534%	$31.1601	$31.16	$31.15	$31.20
Purchase #5	$86.52	5.688%	$91.4413	$91.44	$91.45	$91.40
Purchase #6	$82.51	11.216%	$91.7643	$91.76	$91.75	$91.80
Purchase #7	$91.29	8.543%	$99.0889	$99.09	$99.10	$99.10
7 purchase totals =	$623.85		$688.9633	$688.95	$688.95	$689.00