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	$73.55	12.294%	$82.5922	$82.59	$82.60	$82.60
Purchase #2	$137.89	3.466%	$142.6693	$142.67	$142.65	$142.70
Purchase #3	$155.37	10.788%	$172.1313	$172.13	$172.15	$172.10
Purchase #4	$81.99	12.102%	$91.9124	$91.91	$91.90	$91.90
Purchase #5	$89.88	10.813%	$99.5987	$99.60	$99.60	$99.60
Purchase #6	$120.81	4.239%	$125.9311	$125.93	$125.95	$125.90
Purchase #7	$188.87	10.828%	$209.3208	$209.32	$209.30	$209.30
7 purchase totals =	$848.36		$924.1558	$924.15	$924.15	$924.10