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	$65.82	10.224%	$72.5494	$72.55	$72.55	$72.50
Purchase #2	$208.79	6.735%	$222.852	$222.85	$222.85	$222.90
Purchase #3	$27.47	12.785%	$30.982	$30.98	$31.00	$31.00
Purchase #4	$147.41	12.481%	$165.8082	$165.81	$165.80	$165.80
Purchase #5	$132.98	13.789%	$151.3166	$151.32	$151.30	$151.30
Purchase #6	$110.88	12.285%	$124.5016	$124.50	$124.50	$124.50
Purchase #7	$30.94	6.230%	$32.8676	$32.87	$32.85	$32.90
7 purchase totals =	$724.29		$800.8774	$800.88	$800.85	$800.90