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	$174.51	3.293%	$180.2566	$180.26	$180.25	$180.30
Purchase #2	$248.98	9.138%	$271.7318	$271.73	$271.75	$271.70
Purchase #3	$136.93	9.624%	$150.1081	$150.11	$150.10	$150.10
Purchase #4	$141.68	8.194%	$153.2893	$153.29	$153.30	$153.30
Purchase #5	$38.38	9.165%	$41.8975	$41.90	$41.90	$41.90
Purchase #6	$68.55	5.696%	$72.4546	$72.45	$72.45	$72.50
Purchase #7	$65.69	3.333%	$67.8794	$67.88	$67.90	$67.90
7 purchase totals =	$874.72		$937.6173	$937.62	$937.65	$937.70