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	$109.73	12.733%	$123.7019	$123.70	$123.70	$123.70
Purchase #2	$129.91	9.555%	$142.3229	$142.32	$142.30	$142.30
Purchase #3	$139.30	7.841%	$150.2225	$150.22	$150.20	$150.20
Purchase #4	$6.95	13.619%	$7.8965	$7.90	$7.90	$7.90
Purchase #5	$48.37	12.794%	$54.5585	$54.56	$54.55	$54.60
Purchase #6	$224.85	11.513%	$250.737	$250.74	$250.75	$250.70
Purchase #7	$149.83	9.108%	$163.4765	$163.48	$163.50	$163.50
7 purchase totals =	$808.94		$892.9158	$892.92	$892.90	$892.90