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	$97.86	4.366%	$102.1326	$102.13	$102.15	$102.10
Purchase #2	$99.88	13.744%	$113.6075	$113.61	$113.60	$113.60
Purchase #3	$37.91	8.839%	$41.2609	$41.26	$41.25	$41.30
Purchase #4	$163.39	5.597%	$172.5349	$172.53	$172.55	$172.50
Purchase #5	$85.58	6.216%	$90.8997	$90.90	$90.90	$90.90
Purchase #6	$124.86	11.344%	$139.0241	$139.02	$139.00	$139.00
Purchase #7	$139.98	13.822%	$159.328	$159.33	$159.35	$159.30
7 purchase totals =	$749.46		$818.7877	$818.78	$818.80	$818.70