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	$212.91	5.540%	$224.7052	$224.71	$224.70	$224.70
Purchase #2	$41.77	13.463%	$47.3935	$47.39	$47.40	$47.40
Purchase #3	$93.27	10.316%	$102.8917	$102.89	$102.90	$102.90
Purchase #4	$128.84	8.247%	$139.4654	$139.47	$139.45	$139.50
Purchase #5	$82.74	7.742%	$89.1457	$89.15	$89.15	$89.10
Purchase #6	$113.46	3.270%	$117.1701	$117.17	$117.15	$117.20
Purchase #7	$64.82	9.680%	$71.0946	$71.09	$71.10	$71.10
7 purchase totals =	$737.81		$791.8662	$791.87	$791.85	$791.90