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	$31.25	8.803%	$34.0009	$34.00	$34.00	$34.00
Purchase #2	$140.25	11.704%	$156.6649	$156.66	$156.65	$156.70
Purchase #3	$195.76	10.280%	$215.8841	$215.88	$215.90	$215.90
Purchase #4	$109.45	5.280%	$115.229	$115.23	$115.25	$115.20
Purchase #5	$37.76	4.719%	$39.5419	$39.54	$39.55	$39.50
Purchase #6	$101.47	4.299%	$105.8322	$105.83	$105.85	$105.80
Purchase #7	$20.51	6.848%	$21.9145	$21.91	$21.90	$21.90
7 purchase totals =	$636.45		$689.0675	$689.05	$689.10	$689.00