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	$204.36	5.275%	$215.14	$215.14	$215.15	$215.10
Purchase #2	$241.78	12.410%	$271.7849	$271.78	$271.80	$271.80
Purchase #3	$183.29	4.410%	$191.3731	$191.37	$191.35	$191.40
Purchase #4	$240.81	13.510%	$273.3434	$273.34	$273.35	$273.30
Purchase #5	$164.27	8.805%	$178.734	$178.73	$178.75	$178.70
Purchase #6	$33.84	12.226%	$37.9773	$37.98	$38.00	$38.00
Purchase #7	$187.86	4.842%	$196.9562	$196.96	$196.95	$197.00
7 purchase totals =	$1,256.21		$1,365.3089	$1,365.30	$1,365.35	$1,365.30