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	$81.45	10.152%	$89.7188	$89.72	$89.70	$89.70
Purchase #2	$229.94	12.306%	$258.2364	$258.24	$258.25	$258.20
Purchase #3	$39.96	3.652%	$41.4193	$41.42	$41.40	$41.40
Purchase #4	$211.95	7.777%	$228.4334	$228.43	$228.45	$228.40
Purchase #5	$37.76	3.112%	$38.9351	$38.94	$38.95	$38.90
Purchase #6	$206.44	8.220%	$223.4094	$223.41	$223.40	$223.40
Purchase #7	$39.30	5.426%	$41.4324	$41.43	$41.45	$41.40
7 purchase totals =	$846.80		$921.5848	$921.59	$921.60	$921.40