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	$100.84	12.386%	$113.33	$113.33	$113.35	$113.30
Purchase #2	$226.92	13.330%	$257.1684	$257.17	$257.15	$257.20
Purchase #3	$199.43	10.797%	$220.9625	$220.96	$220.95	$221.00
Purchase #4	$108.87	8.745%	$118.3907	$118.39	$118.40	$118.40
Purchase #5	$25.50	6.306%	$27.108	$27.11	$27.10	$27.10
Purchase #6	$43.27	5.392%	$45.6031	$45.60	$45.60	$45.60
Purchase #7	$53.84	11.228%	$59.8852	$59.89	$59.90	$59.90
7 purchase totals =	$758.67		$842.4479	$842.45	$842.45	$842.50