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	$149.81	12.282%	$168.2097	$168.21	$168.20	$168.20
Purchase #2	$29.80	10.626%	$32.9665	$32.97	$32.95	$33.00
Purchase #3	$116.91	12.673%	$131.726	$131.73	$131.75	$131.70
Purchase #4	$204.67	5.207%	$215.3272	$215.33	$215.35	$215.30
Purchase #5	$68.86	13.826%	$78.3806	$78.38	$78.40	$78.40
Purchase #6	$127.41	6.834%	$136.1172	$136.12	$136.10	$136.10
Purchase #7	$98.58	10.296%	$108.7298	$108.73	$108.75	$108.70
7 purchase totals =	$796.04		$871.4570	$871.47	$871.50	$871.40