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	$213.46	4.581%	$223.2386	$223.24	$223.25	$223.20
Purchase #2	$221.60	13.180%	$250.8069	$250.81	$250.80	$250.80
Purchase #3	$10.97	4.504%	$11.4641	$11.46	$11.45	$11.50
Purchase #4	$83.57	13.160%	$94.5678	$94.57	$94.55	$94.60
Purchase #5	$36.99	13.566%	$42.0081	$42.01	$42.00	$42.00
Purchase #6	$72.49	5.344%	$76.3639	$76.36	$76.35	$76.40
Purchase #7	$142.70	11.334%	$158.8736	$158.87	$158.85	$158.90
7 purchase totals =	$781.78		$857.3230	$857.32	$857.25	$857.40