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	$127.48	11.793%	$142.5137	$142.51	$142.50	$142.50
Purchase #2	$28.57	11.614%	$31.8881	$31.89	$31.90	$31.90
Purchase #3	$173.72	7.174%	$186.1827	$186.18	$186.20	$186.20
Purchase #4	$122.74	7.358%	$131.7712	$131.77	$131.75	$131.80
Purchase #5	$102.51	7.130%	$109.819	$109.82	$109.80	$109.80
Purchase #6	$103.88	11.500%	$115.8262	$115.83	$115.85	$115.80
Purchase #7	$141.34	9.749%	$155.1192	$155.12	$155.10	$155.10
7 purchase totals =	$800.24		$873.1201	$873.12	$873.10	$873.10