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	$157.43	8.692%	$171.1138	$171.11	$171.10	$171.10
Purchase #2	$109.49	5.283%	$115.2744	$115.27	$115.25	$115.30
Purchase #3	$107.84	10.123%	$118.7566	$118.76	$118.75	$118.80
Purchase #4	$137.85	9.503%	$150.9499	$150.95	$150.95	$150.90
Purchase #5	$112.61	8.825%	$122.5478	$122.55	$122.55	$122.50
Purchase #6	$72.73	13.306%	$82.4075	$82.41	$82.40	$82.40
Purchase #7	$78.31	5.841%	$82.8841	$82.88	$82.90	$82.90
7 purchase totals =	$776.26		$843.9341	$843.93	$843.90	$843.90