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	$6.45	6.276%	$6.8548	$6.85	$6.85	$6.90
Purchase #2	$244.79	12.465%	$275.3031	$275.30	$275.30	$275.30
Purchase #3	$67.91	6.696%	$72.4573	$72.46	$72.45	$72.50
Purchase #4	$239.65	5.455%	$252.7229	$252.72	$252.70	$252.70
Purchase #5	$163.60	6.813%	$174.7461	$174.75	$174.75	$174.70
Purchase #6	$144.88	7.364%	$155.549	$155.55	$155.55	$155.50
Purchase #7	$169.90	9.333%	$185.7568	$185.76	$185.75	$185.80
7 purchase totals =	$1,037.18		$1,123.3900	$1,123.39	$1,123.35	$1,123.40