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	$33.91	13.850%	$38.6065	$38.61	$38.60	$38.60
Purchase #2	$229.71	11.236%	$255.5202	$255.52	$255.50	$255.50
Purchase #3	$235.74	4.190%	$245.6175	$245.62	$245.60	$245.60
Purchase #4	$91.52	8.828%	$99.5994	$99.60	$99.60	$99.60
Purchase #5	$101.27	3.474%	$104.7881	$104.79	$104.80	$104.80
Purchase #6	$116.62	10.207%	$128.5234	$128.52	$128.50	$128.50
Purchase #7	$78.88	10.147%	$86.884	$86.88	$86.90	$86.90
7 purchase totals =	$887.65		$959.5391	$959.54	$959.50	$959.50