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	$174.71	3.174%	$180.2553	$180.26	$180.25	$180.30
Purchase #2	$199.64	11.781%	$223.1596	$223.16	$223.15	$223.20
Purchase #3	$34.45	12.864%	$38.8816	$38.88	$38.90	$38.90
Purchase #4	$234.71	13.117%	$265.4969	$265.50	$265.50	$265.50
Purchase #5	$19.43	8.830%	$21.1457	$21.15	$21.15	$21.10
Purchase #6	$49.96	13.438%	$56.6736	$56.67	$56.65	$56.70
Purchase #7	$63.33	13.337%	$71.7763	$71.78	$71.80	$71.80
7 purchase totals =	$776.23		$857.3890	$857.40	$857.40	$857.50