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	$229.53	13.179%	$259.7798	$259.78	$259.80	$259.80
Purchase #2	$99.90	5.432%	$105.3266	$105.33	$105.35	$105.30
Purchase #3	$176.37	9.208%	$192.6101	$192.61	$192.60	$192.60
Purchase #4	$57.82	6.479%	$61.5662	$61.57	$61.55	$61.60
Purchase #5	$182.35	9.284%	$199.2794	$199.28	$199.30	$199.30
Purchase #6	$68.61	6.294%	$72.9283	$72.93	$72.95	$72.90
Purchase #7	$33.54	8.398%	$36.3567	$36.36	$36.35	$36.40
7 purchase totals =	$848.12		$927.8471	$927.86	$927.90	$927.90