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	$196.86	6.826%	$210.2977	$210.30	$210.30	$210.30
Purchase #2	$153.33	13.485%	$174.0066	$174.01	$174.00	$174.00
Purchase #3	$47.32	5.458%	$49.9027	$49.90	$49.90	$49.90
Purchase #4	$123.93	5.685%	$130.9754	$130.98	$131.00	$131.00
Purchase #5	$101.60	12.515%	$114.3152	$114.32	$114.30	$114.30
Purchase #6	$141.62	13.626%	$160.9171	$160.92	$160.90	$160.90
Purchase #7	$53.64	4.296%	$55.9444	$55.94	$55.95	$55.90
7 purchase totals =	$818.30		$896.3591	$896.37	$896.35	$896.30