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	$65.96	6.414%	$70.1907	$70.19	$70.20	$70.20
Purchase #2	$176.39	3.191%	$182.0186	$182.02	$182.00	$182.00
Purchase #3	$208.56	4.740%	$218.4457	$218.45	$218.45	$218.40
Purchase #4	$112.93	9.855%	$124.0593	$124.06	$124.05	$124.10
Purchase #5	$64.79	8.389%	$70.2252	$70.23	$70.25	$70.20
Purchase #6	$162.92	11.248%	$181.2452	$181.25	$181.25	$181.20
Purchase #7	$120.58	9.401%	$131.9157	$131.92	$131.90	$131.90
7 purchase totals =	$912.13		$978.1004	$978.12	$978.10	$978.00