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	$134.51	4.684%	$140.8104	$140.81	$140.80	$140.80
Purchase #2	$218.98	10.740%	$242.4985	$242.50	$242.50	$242.50
Purchase #3	$175.25	9.278%	$191.5097	$191.51	$191.50	$191.50
Purchase #4	$203.32	12.765%	$229.2738	$229.27	$229.25	$229.30
Purchase #5	$106.68	9.457%	$116.7687	$116.77	$116.75	$116.80
Purchase #6	$131.66	9.258%	$143.8491	$143.85	$143.85	$143.80
Purchase #7	$183.54	3.851%	$190.6081	$190.61	$190.60	$190.60
7 purchase totals =	$1,153.94		$1,255.3183	$1,255.32	$1,255.25	$1,255.30