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	$228.53	12.663%	$257.4688	$257.47	$257.45	$257.50
Purchase #2	$78.88	8.486%	$85.5738	$85.57	$85.55	$85.60
Purchase #3	$182.91	7.103%	$195.9021	$195.90	$195.90	$195.90
Purchase #4	$119.67	6.592%	$127.5586	$127.56	$127.55	$127.60
Purchase #5	$14.99	6.855%	$16.0176	$16.02	$16.00	$16.00
Purchase #6	$183.79	4.166%	$191.4467	$191.45	$191.45	$191.40
Purchase #7	$95.46	4.241%	$99.5085	$99.51	$99.50	$99.50
7 purchase totals =	$904.23		$973.4761	$973.48	$973.40	$973.50