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	$72.49	9.197%	$79.1569	$79.16	$79.15	$79.20
Purchase #2	$130.34	10.511%	$144.04	$144.04	$144.05	$144.00
Purchase #3	$158.90	13.647%	$180.5851	$180.59	$180.60	$180.60
Purchase #4	$210.48	3.359%	$217.55	$217.55	$217.55	$217.60
Purchase #5	$82.57	4.127%	$85.9777	$85.98	$86.00	$86.00
Purchase #6	$104.48	7.695%	$112.5197	$112.52	$112.50	$112.50
Purchase #7	$156.53	10.844%	$173.5041	$173.50	$173.50	$173.50
7 purchase totals =	$915.79		$993.3335	$993.34	$993.35	$993.40