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	$72.74	9.418%	$79.5907	$79.59	$79.60	$79.60
Purchase #2	$64.50	10.820%	$71.4789	$71.48	$71.50	$71.50
Purchase #3	$154.59	5.418%	$162.9657	$162.97	$162.95	$163.00
Purchase #4	$115.53	13.632%	$131.279	$131.28	$131.30	$131.30
Purchase #5	$60.27	8.487%	$65.3851	$65.39	$65.40	$65.40
Purchase #6	$119.89	8.593%	$130.1921	$130.19	$130.20	$130.20
Purchase #7	$200.79	11.591%	$224.0636	$224.06	$224.05	$224.10
7 purchase totals =	$788.31		$864.9551	$864.96	$865.00	$865.10