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	$162.78	4.710%	$170.4469	$170.45	$170.45	$170.40
Purchase #2	$119.27	13.174%	$134.9826	$134.98	$135.00	$135.00
Purchase #3	$70.87	4.185%	$73.8359	$73.84	$73.85	$73.80
Purchase #4	$73.77	10.473%	$81.4959	$81.50	$81.50	$81.50
Purchase #5	$52.89	13.189%	$59.8657	$59.87	$59.85	$59.90
Purchase #6	$18.96	4.795%	$19.8691	$19.87	$19.85	$19.90
Purchase #7	$124.33	7.810%	$134.0402	$134.04	$134.05	$134.00
7 purchase totals =	$622.87		$674.5363	$674.55	$674.55	$674.50