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	$141.80	10.628%	$156.8705	$156.87	$156.85	$156.90
Purchase #2	$77.54	11.352%	$86.3423	$86.34	$86.35	$86.30
Purchase #3	$38.53	10.574%	$42.6042	$42.60	$42.60	$42.60
Purchase #4	$123.37	10.333%	$136.1178	$136.12	$136.10	$136.10
Purchase #5	$182.89	4.324%	$190.7982	$190.80	$190.80	$190.80
Purchase #6	$18.56	7.813%	$20.0101	$20.01	$20.00	$20.00
Purchase #7	$60.77	6.670%	$64.8234	$64.82	$64.80	$64.80
7 purchase totals =	$643.46		$697.5665	$697.56	$697.50	$697.50