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	$222.50	7.840%	$239.944	$239.94	$239.95	$239.90
Purchase #2	$84.60	7.440%	$90.8942	$90.89	$90.90	$90.90
Purchase #3	$32.72	10.514%	$36.1602	$36.16	$36.15	$36.20
Purchase #4	$115.77	12.601%	$130.3582	$130.36	$130.35	$130.40
Purchase #5	$54.61	9.558%	$59.8296	$59.83	$59.85	$59.80
Purchase #6	$232.70	10.499%	$257.1312	$257.13	$257.15	$257.10
Purchase #7	$91.92	13.224%	$104.0755	$104.08	$104.10	$104.10
7 purchase totals =	$834.82		$918.3929	$918.39	$918.45	$918.40