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	$37.53	5.203%	$39.4827	$39.48	$39.50	$39.50
Purchase #2	$234.69	9.126%	$256.1078	$256.11	$256.10	$256.10
Purchase #3	$139.58	3.416%	$144.3481	$144.35	$144.35	$144.30
Purchase #4	$138.78	6.356%	$147.6009	$147.60	$147.60	$147.60
Purchase #5	$212.59	4.809%	$222.8135	$222.81	$222.80	$222.80
Purchase #6	$36.27	13.285%	$41.0885	$41.09	$41.10	$41.10
Purchase #7	$67.81	5.473%	$71.5212	$71.52	$71.50	$71.50
7 purchase totals =	$867.25		$922.9627	$922.96	$922.95	$922.90