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	$74.86	4.768%	$78.4293	$78.43	$78.45	$78.40
Purchase #2	$158.61	12.741%	$178.8185	$178.82	$178.80	$178.80
Purchase #3	$192.78	9.362%	$210.8281	$210.83	$210.85	$210.80
Purchase #4	$48.37	11.312%	$53.8416	$53.84	$53.85	$53.80
Purchase #5	$112.34	10.841%	$124.5188	$124.52	$124.50	$124.50
Purchase #6	$55.69	5.161%	$58.5642	$58.56	$58.55	$58.60
Purchase #7	$209.66	9.602%	$229.7916	$229.79	$229.80	$229.80
7 purchase totals =	$852.31		$934.7921	$934.79	$934.80	$934.70