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	$165.52	3.220%	$170.8497	$170.85	$170.85	$170.80
Purchase #2	$210.63	3.560%	$218.1284	$218.13	$218.15	$218.10
Purchase #3	$65.34	9.443%	$71.5101	$71.51	$71.50	$71.50
Purchase #4	$63.66	12.355%	$71.5252	$71.53	$71.55	$71.50
Purchase #5	$118.57	8.431%	$128.5666	$128.57	$128.55	$128.60
Purchase #6	$67.92	12.429%	$76.3618	$76.36	$76.35	$76.40
Purchase #7	$145.64	5.724%	$153.9764	$153.98	$154.00	$154.00
7 purchase totals =	$837.28		$890.9182	$890.93	$890.95	$890.90