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	$52.61	13.220%	$59.565	$59.57	$59.55	$59.60
Purchase #2	$242.82	10.828%	$269.1125	$269.11	$269.10	$269.10
Purchase #3	$168.47	9.600%	$184.6431	$184.64	$184.65	$184.60
Purchase #4	$134.62	3.331%	$139.1042	$139.10	$139.10	$139.10
Purchase #5	$178.94	13.787%	$203.6105	$203.61	$203.60	$203.60
Purchase #6	$159.57	4.216%	$166.2975	$166.30	$166.30	$166.30
Purchase #7	$227.72	12.185%	$255.4677	$255.47	$255.45	$255.50
7 purchase totals =	$1,164.75		$1,277.8005	$1,277.80	$1,277.75	$1,277.80