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	$91.31	9.146%	$99.6612	$99.66	$99.65	$99.70
Purchase #2	$124.90	8.776%	$135.8612	$135.86	$135.85	$135.90
Purchase #3	$120.93	11.558%	$134.9071	$134.91	$134.90	$134.90
Purchase #4	$94.82	7.439%	$101.8737	$101.87	$101.85	$101.90
Purchase #5	$93.78	10.225%	$103.369	$103.37	$103.35	$103.40
Purchase #6	$212.59	4.821%	$222.839	$222.84	$222.85	$222.80
Purchase #7	$39.71	6.493%	$42.2884	$42.29	$42.30	$42.30
7 purchase totals =	$778.04		$840.7996	$840.80	$840.75	$840.90