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	$123.72	6.515%	$131.7804	$131.78	$131.80	$131.80
Purchase #2	$77.69	3.745%	$80.5995	$80.60	$80.60	$80.60
Purchase #3	$92.97	12.282%	$104.3886	$104.39	$104.40	$104.40
Purchase #4	$82.77	11.802%	$92.5385	$92.54	$92.55	$92.50
Purchase #5	$8.63	6.534%	$9.1939	$9.19	$9.20	$9.20
Purchase #6	$149.30	12.195%	$167.5071	$167.51	$167.50	$167.50
Purchase #7	$162.82	6.178%	$172.879	$172.88	$172.90	$172.90
7 purchase totals =	$697.90		$758.8870	$758.89	$758.95	$758.90