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	$76.58	12.721%	$86.3217	$86.32	$86.30	$86.30
Purchase #2	$58.41	6.671%	$62.3065	$62.31	$62.30	$62.30
Purchase #3	$29.80	6.799%	$31.8261	$31.83	$31.85	$31.80
Purchase #4	$135.30	6.328%	$143.8618	$143.86	$143.85	$143.90
Purchase #5	$170.62	11.246%	$189.8079	$189.81	$189.80	$189.80
Purchase #6	$172.82	4.680%	$180.908	$180.91	$180.90	$180.90
Purchase #7	$131.78	11.631%	$147.1073	$147.11	$147.10	$147.10
7 purchase totals =	$775.31		$842.1393	$842.15	$842.10	$842.10