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	$66.77	5.559%	$70.4817	$70.48	$70.50	$70.50
Purchase #2	$78.69	12.144%	$88.2461	$88.25	$88.25	$88.20
Purchase #3	$57.50	13.559%	$65.2964	$65.30	$65.30	$65.30
Purchase #4	$181.25	7.228%	$194.3508	$194.35	$194.35	$194.40
Purchase #5	$182.56	12.823%	$205.9697	$205.97	$205.95	$206.00
Purchase #6	$59.65	13.806%	$67.8853	$67.89	$67.90	$67.90
Purchase #7	$238.88	6.156%	$253.5855	$253.59	$253.60	$253.60
7 purchase totals =	$865.30		$945.8155	$945.83	$945.85	$945.90