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	$111.89	10.698%	$123.86	$123.86	$123.85	$123.90
Purchase #2	$127.44	3.407%	$131.7819	$131.78	$131.80	$131.80
Purchase #3	$121.47	11.665%	$135.6395	$135.64	$135.65	$135.60
Purchase #4	$67.90	12.588%	$76.4473	$76.45	$76.45	$76.40
Purchase #5	$45.43	4.812%	$47.6161	$47.62	$47.60	$47.60
Purchase #6	$213.71	5.443%	$225.3422	$225.34	$225.35	$225.30
Purchase #7	$104.96	12.764%	$118.3571	$118.36	$118.35	$118.40
7 purchase totals =	$792.80		$859.0441	$859.05	$859.05	$859.00