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	$249.57	6.402%	$265.5475	$265.55	$265.55	$265.50
Purchase #2	$54.84	3.157%	$56.5713	$56.57	$56.55	$56.60
Purchase #3	$85.26	11.873%	$95.3829	$95.38	$95.40	$95.40
Purchase #4	$32.89	10.409%	$36.3135	$36.31	$36.30	$36.30
Purchase #5	$200.96	13.309%	$227.7058	$227.71	$227.70	$227.70
Purchase #6	$51.79	4.498%	$54.1195	$54.12	$54.10	$54.10
Purchase #7	$37.59	8.659%	$40.8449	$40.84	$40.85	$40.80
7 purchase totals =	$712.90		$776.4854	$776.48	$776.45	$776.40