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	$50.61	10.234%	$55.7894	$55.79	$55.80	$55.80
Purchase #2	$124.63	8.220%	$134.8746	$134.87	$134.85	$134.90
Purchase #3	$170.76	12.396%	$191.9274	$191.93	$191.95	$191.90
Purchase #4	$42.38	13.842%	$48.2462	$48.25	$48.25	$48.20
Purchase #5	$233.77	13.734%	$265.876	$265.88	$265.90	$265.90
Purchase #6	$34.65	12.547%	$38.9975	$39.00	$39.00	$39.00
Purchase #7	$66.74	8.793%	$72.6084	$72.61	$72.60	$72.60
7 purchase totals =	$723.54		$808.3195	$808.33	$808.35	$808.30