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	$138.69	5.505%	$146.3249	$146.32	$146.30	$146.30
Purchase #2	$55.68	6.517%	$59.3087	$59.31	$59.30	$59.30
Purchase #3	$142.68	3.288%	$147.3713	$147.37	$147.35	$147.40
Purchase #4	$142.90	13.763%	$162.5673	$162.57	$162.55	$162.60
Purchase #5	$172.95	12.660%	$194.8455	$194.85	$194.85	$194.80
Purchase #6	$186.90	13.788%	$212.6698	$212.67	$212.65	$212.70
Purchase #7	$88.90	3.300%	$91.8337	$91.83	$91.85	$91.80
7 purchase totals =	$928.70		$1,014.9212	$1,014.92	$1,014.85	$1,014.90