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	$133.86	4.284%	$139.5946	$139.59	$139.60	$139.60
Purchase #2	$55.73	8.700%	$60.5785	$60.58	$60.60	$60.60
Purchase #3	$99.35	7.204%	$106.5072	$106.51	$106.50	$106.50
Purchase #4	$80.56	13.630%	$91.5403	$91.54	$91.55	$91.50
Purchase #5	$150.87	3.606%	$156.3104	$156.31	$156.30	$156.30
Purchase #6	$55.63	13.535%	$63.1595	$63.16	$63.15	$63.20
Purchase #7	$7.88	10.706%	$8.7236	$8.72	$8.70	$8.70
7 purchase totals =	$583.88		$626.4141	$626.41	$626.40	$626.40