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	$136.91	8.556%	$148.624	$148.62	$148.60	$148.60
Purchase #2	$83.54	3.588%	$86.5374	$86.54	$86.55	$86.50
Purchase #3	$91.73	12.599%	$103.2871	$103.29	$103.30	$103.30
Purchase #4	$91.62	10.421%	$101.1677	$101.17	$101.15	$101.20
Purchase #5	$56.66	3.181%	$58.4624	$58.46	$58.45	$58.50
Purchase #6	$227.89	13.304%	$258.2085	$258.21	$258.20	$258.20
Purchase #7	$105.56	11.417%	$117.6118	$117.61	$117.60	$117.60
7 purchase totals =	$793.91		$873.8989	$873.90	$873.85	$873.90