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	$183.25	3.314%	$189.3229	$189.32	$189.30	$189.30
Purchase #2	$58.41	12.175%	$65.5214	$65.52	$65.50	$65.50
Purchase #3	$78.90	4.585%	$82.5176	$82.52	$82.50	$82.50
Purchase #4	$143.95	6.737%	$153.6479	$153.65	$153.65	$153.60
Purchase #5	$24.42	12.733%	$27.5294	$27.53	$27.55	$27.50
Purchase #6	$29.62	7.667%	$31.891	$31.89	$31.90	$31.90
Purchase #7	$236.77	9.157%	$258.451	$258.45	$258.45	$258.50
7 purchase totals =	$755.32		$808.8812	$808.88	$808.85	$808.80