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	$207.85	11.562%	$231.8816	$231.88	$231.90	$231.90
Purchase #2	$116.78	10.820%	$129.4156	$129.42	$129.40	$129.40
Purchase #3	$122.51	7.608%	$131.8306	$131.83	$131.85	$131.80
Purchase #4	$33.98	7.416%	$36.5	$36.50	$36.50	$36.50
Purchase #5	$134.94	5.361%	$142.1741	$142.17	$142.15	$142.20
Purchase #6	$140.36	8.245%	$151.9327	$151.93	$151.95	$151.90
Purchase #7	$34.95	6.576%	$37.2483	$37.25	$37.25	$37.20
7 purchase totals =	$791.37		$860.9829	$860.98	$861.00	$860.90