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	$235.27	12.327%	$264.2717	$264.27	$264.25	$264.30
Purchase #2	$78.50	5.874%	$83.1111	$83.11	$83.10	$83.10
Purchase #3	$248.81	6.726%	$265.545	$265.55	$265.55	$265.50
Purchase #4	$176.40	10.294%	$194.5586	$194.56	$194.55	$194.60
Purchase #5	$163.58	3.251%	$168.898	$168.90	$168.90	$168.90
Purchase #6	$136.78	8.669%	$148.6375	$148.64	$148.65	$148.60
Purchase #7	$96.45	7.671%	$103.8487	$103.85	$103.85	$103.80
7 purchase totals =	$1,135.79		$1,228.8706	$1,228.88	$1,228.85	$1,228.80