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	$125.33	12.192%	$140.6102	$140.61	$140.60	$140.60
Purchase #2	$128.34	11.228%	$142.75	$142.75	$142.75	$142.80
Purchase #3	$103.71	8.471%	$112.4953	$112.50	$112.50	$112.50
Purchase #4	$39.74	5.395%	$41.884	$41.88	$41.90	$41.90
Purchase #5	$127.77	4.864%	$133.9847	$133.98	$134.00	$134.00
Purchase #6	$124.94	4.440%	$130.4873	$130.49	$130.50	$130.50
Purchase #7	$123.26	4.181%	$128.4135	$128.41	$128.40	$128.40
7 purchase totals =	$773.09		$830.6250	$830.62	$830.65	$830.70