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	$40.78	3.296%	$42.1241	$42.12	$42.10	$42.10
Purchase #2	$82.38	9.494%	$90.2012	$90.20	$90.20	$90.20
Purchase #3	$156.72	6.824%	$167.4146	$167.41	$167.40	$167.40
Purchase #4	$232.62	4.479%	$243.039	$243.04	$243.05	$243.00
Purchase #5	$80.53	8.434%	$87.3219	$87.32	$87.30	$87.30
Purchase #6	$202.28	11.157%	$224.8484	$224.85	$224.85	$224.80
Purchase #7	$34.62	9.333%	$37.8511	$37.85	$37.85	$37.90
7 purchase totals =	$829.93		$892.8003	$892.79	$892.75	$892.70