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	$37.66	12.206%	$42.2568	$42.26	$42.25	$42.30
Purchase #2	$50.50	7.754%	$54.4158	$54.42	$54.40	$54.40
Purchase #3	$148.34	9.465%	$162.3804	$162.38	$162.40	$162.40
Purchase #4	$146.82	12.288%	$164.8612	$164.86	$164.85	$164.90
Purchase #5	$188.46	13.746%	$214.3657	$214.37	$214.35	$214.40
Purchase #6	$65.46	12.350%	$73.5443	$73.54	$73.55	$73.50
Purchase #7	$24.88	9.639%	$27.2782	$27.28	$27.30	$27.30
7 purchase totals =	$662.12		$739.1024	$739.11	$739.10	$739.20