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	$29.43	13.611%	$33.4357	$33.44	$33.45	$33.40
Purchase #2	$206.68	10.860%	$229.1254	$229.13	$229.15	$229.10
Purchase #3	$59.32	8.396%	$64.3005	$64.30	$64.30	$64.30
Purchase #4	$46.50	12.860%	$52.4799	$52.48	$52.50	$52.50
Purchase #5	$117.62	11.710%	$131.3933	$131.39	$131.40	$131.40
Purchase #6	$33.71	8.280%	$36.5012	$36.50	$36.50	$36.50
Purchase #7	$66.43	11.173%	$73.8522	$73.85	$73.85	$73.90
7 purchase totals =	$559.69		$621.0882	$621.09	$621.15	$621.10