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	$157.46	8.596%	$170.9953	$171.00	$171.00	$171.00
Purchase #2	$196.90	4.782%	$206.3158	$206.32	$206.30	$206.30
Purchase #3	$71.92	9.132%	$78.4877	$78.49	$78.50	$78.50
Purchase #4	$32.60	11.667%	$36.4034	$36.40	$36.40	$36.40
Purchase #5	$185.39	6.575%	$197.5794	$197.58	$197.60	$197.60
Purchase #6	$68.80	8.347%	$74.5427	$74.54	$74.55	$74.50
Purchase #7	$229.69	10.541%	$253.9016	$253.90	$253.90	$253.90
7 purchase totals =	$942.76		$1,018.2259	$1,018.23	$1,018.25	$1,018.20