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	$106.43	6.763%	$113.6279	$113.63	$113.65	$113.60
Purchase #2	$150.37	8.325%	$162.8883	$162.89	$162.90	$162.90
Purchase #3	$83.40	4.178%	$86.8845	$86.88	$86.90	$86.90
Purchase #4	$52.87	9.803%	$58.0528	$58.05	$58.05	$58.10
Purchase #5	$81.92	11.537%	$91.3711	$91.37	$91.35	$91.40
Purchase #6	$110.77	11.771%	$123.8087	$123.81	$123.80	$123.80
Purchase #7	$25.32	12.764%	$28.5518	$28.55	$28.55	$28.60
7 purchase totals =	$611.08		$665.1851	$665.18	$665.20	$665.30