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	$149.99	10.383%	$165.5635	$165.56	$165.55	$165.60
Purchase #2	$227.79	8.245%	$246.5713	$246.57	$246.55	$246.60
Purchase #3	$40.81	4.874%	$42.7991	$42.80	$42.80	$42.80
Purchase #4	$55.92	11.814%	$62.5264	$62.53	$62.55	$62.50
Purchase #5	$38.48	6.240%	$40.8812	$40.88	$40.90	$40.90
Purchase #6	$122.56	13.307%	$138.8691	$138.87	$138.85	$138.90
Purchase #7	$85.50	11.112%	$95.0008	$95.00	$95.00	$95.00
7 purchase totals =	$721.05		$792.2114	$792.21	$792.20	$792.30