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	$62.76	5.494%	$66.208	$66.21	$66.20	$66.20
Purchase #2	$164.33	11.254%	$182.8237	$182.82	$182.80	$182.80
Purchase #3	$43.32	4.743%	$45.3747	$45.37	$45.35	$45.40
Purchase #4	$154.84	12.683%	$174.4784	$174.48	$174.50	$174.50
Purchase #5	$57.65	4.550%	$60.2731	$60.27	$60.25	$60.30
Purchase #6	$136.56	8.836%	$148.6264	$148.63	$148.65	$148.60
Purchase #7	$86.63	6.741%	$92.4697	$92.47	$92.45	$92.50
7 purchase totals =	$706.09		$770.2540	$770.25	$770.20	$770.30