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	$52.53	8.709%	$57.1048	$57.10	$57.10	$57.10
Purchase #2	$137.94	3.701%	$143.0452	$143.05	$143.05	$143.00
Purchase #3	$250.32	5.707%	$264.6058	$264.61	$264.60	$264.60
Purchase #4	$92.79	10.237%	$102.2889	$102.29	$102.30	$102.30
Purchase #5	$162.73	7.222%	$174.4824	$174.48	$174.50	$174.50
Purchase #6	$22.92	12.414%	$25.7653	$25.77	$25.75	$25.80
Purchase #7	$195.38	13.862%	$222.4636	$222.46	$222.45	$222.50
7 purchase totals =	$914.61		$989.7560	$989.76	$989.75	$989.80