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	$209.78	3.730%	$217.6048	$217.60	$217.60	$217.60
Purchase #2	$233.42	13.481%	$264.8874	$264.89	$264.90	$264.90
Purchase #3	$148.56	5.747%	$157.0977	$157.10	$157.10	$157.10
Purchase #4	$212.46	10.597%	$234.9744	$234.97	$234.95	$235.00
Purchase #5	$127.46	10.282%	$140.5654	$140.57	$140.55	$140.60
Purchase #6	$72.75	10.725%	$80.5524	$80.55	$80.55	$80.60
Purchase #7	$162.96	13.543%	$185.0297	$185.03	$185.05	$185.00
7 purchase totals =	$1,167.39		$1,280.7118	$1,280.71	$1,280.70	$1,280.80