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	$31.64	4.290%	$32.9974	$33.00	$33.00	$33.00
Purchase #2	$209.78	12.310%	$235.6039	$235.60	$235.60	$235.60
Purchase #3	$129.90	7.763%	$139.9841	$139.98	$140.00	$140.00
Purchase #4	$110.29	8.806%	$120.0021	$120.00	$120.00	$120.00
Purchase #5	$175.45	8.425%	$190.2317	$190.23	$190.25	$190.20
Purchase #6	$33.72	12.288%	$37.8635	$37.86	$37.85	$37.90
Purchase #7	$37.26	6.153%	$39.5526	$39.55	$39.55	$39.60
7 purchase totals =	$728.04		$796.2353	$796.22	$796.25	$796.30