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	$180.36	3.612%	$186.8746	$186.87	$186.85	$186.90
Purchase #2	$142.39	3.604%	$147.5217	$147.52	$147.50	$147.50
Purchase #3	$92.49	7.460%	$99.3898	$99.39	$99.40	$99.40
Purchase #4	$59.56	11.874%	$66.6322	$66.63	$66.65	$66.60
Purchase #5	$81.59	8.147%	$88.2371	$88.24	$88.25	$88.20
Purchase #6	$138.92	9.833%	$152.58	$152.58	$152.60	$152.60
Purchase #7	$101.89	13.285%	$115.4261	$115.43	$115.45	$115.40
7 purchase totals =	$797.20		$856.6615	$856.66	$856.70	$856.60