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	$134.78	7.841%	$145.3481	$145.35	$145.35	$145.30
Purchase #2	$75.29	9.653%	$82.5577	$82.56	$82.55	$82.60
Purchase #3	$112.58	5.865%	$119.1828	$119.18	$119.20	$119.20
Purchase #4	$117.28	10.383%	$129.4572	$129.46	$129.45	$129.50
Purchase #5	$205.26	8.780%	$223.2818	$223.28	$223.30	$223.30
Purchase #6	$92.31	3.209%	$95.2722	$95.27	$95.25	$95.30
Purchase #7	$118.28	8.496%	$128.3291	$128.33	$128.35	$128.30
7 purchase totals =	$855.78		$923.4289	$923.43	$923.45	$923.50