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	$45.96	13.793%	$52.2993	$52.30	$52.30	$52.30
Purchase #2	$185.92	13.782%	$211.5435	$211.54	$211.55	$211.50
Purchase #3	$16.60	11.845%	$18.5663	$18.57	$18.55	$18.60
Purchase #4	$40.59	3.758%	$42.1154	$42.12	$42.10	$42.10
Purchase #5	$191.39	7.278%	$205.3194	$205.32	$205.30	$205.30
Purchase #6	$19.58	3.793%	$20.3227	$20.32	$20.30	$20.30
Purchase #7	$248.48	8.812%	$270.3761	$270.38	$270.40	$270.40
7 purchase totals =	$748.52		$820.5427	$820.55	$820.50	$820.50