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	$75.31	9.534%	$82.4901	$82.49	$82.50	$82.50
Purchase #2	$117.71	9.496%	$128.8877	$128.89	$128.90	$128.90
Purchase #3	$103.61	12.348%	$116.4038	$116.40	$116.40	$116.40
Purchase #4	$25.59	3.549%	$26.4982	$26.50	$26.50	$26.50
Purchase #5	$154.50	13.458%	$175.2926	$175.29	$175.30	$175.30
Purchase #6	$195.57	8.104%	$211.419	$211.42	$211.40	$211.40
Purchase #7	$25.61	10.822%	$28.3815	$28.38	$28.40	$28.40
7 purchase totals =	$697.90		$769.3729	$769.37	$769.40	$769.40