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	$44.96	10.657%	$49.7514	$49.75	$49.75	$49.80
Purchase #2	$239.34	6.765%	$255.5314	$255.53	$255.55	$255.50
Purchase #3	$68.82	13.403%	$78.0439	$78.04	$78.05	$78.00
Purchase #4	$185.51	4.751%	$194.3236	$194.32	$194.30	$194.30
Purchase #5	$33.70	11.419%	$37.5482	$37.55	$37.55	$37.50
Purchase #6	$248.55	7.629%	$267.5119	$267.51	$267.50	$267.50
Purchase #7	$117.93	4.456%	$123.185	$123.19	$123.20	$123.20
7 purchase totals =	$938.81		$1,005.8954	$1,005.89	$1,005.90	$1,005.80