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	$29.41	7.136%	$31.5087	$31.51	$31.50	$31.50
Purchase #2	$51.81	7.583%	$55.7388	$55.74	$55.75	$55.70
Purchase #3	$143.31	12.263%	$160.8841	$160.88	$160.90	$160.90
Purchase #4	$239.59	10.365%	$264.4235	$264.42	$264.40	$264.40
Purchase #5	$44.36	4.280%	$46.2586	$46.26	$46.25	$46.30
Purchase #6	$168.42	12.725%	$189.8514	$189.85	$189.85	$189.90
Purchase #7	$61.97	7.530%	$66.6363	$66.64	$66.65	$66.60
7 purchase totals =	$738.87		$815.3014	$815.30	$815.30	$815.30