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	$79.30	6.322%	$84.3133	$84.31	$84.30	$84.30
Purchase #2	$41.82	6.397%	$44.4952	$44.50	$44.50	$44.50
Purchase #3	$166.43	4.756%	$174.3454	$174.35	$174.35	$174.30
Purchase #4	$34.95	8.302%	$37.8515	$37.85	$37.85	$37.90
Purchase #5	$99.61	5.329%	$104.9182	$104.92	$104.90	$104.90
Purchase #6	$182.42	7.142%	$195.4484	$195.45	$195.45	$195.40
Purchase #7	$61.89	3.213%	$63.8785	$63.88	$63.90	$63.90
7 purchase totals =	$666.42		$705.2505	$705.26	$705.25	$705.20