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	$37.35	7.865%	$40.2876	$40.29	$40.30	$40.30
Purchase #2	$245.34	11.609%	$273.8215	$273.82	$273.80	$273.80
Purchase #3	$29.37	8.468%	$31.8571	$31.86	$31.85	$31.90
Purchase #4	$217.93	5.290%	$229.4585	$229.46	$229.45	$229.50
Purchase #5	$22.92	6.836%	$24.4868	$24.49	$24.50	$24.50
Purchase #6	$69.29	6.826%	$74.0197	$74.02	$74.00	$74.00
Purchase #7	$90.43	6.123%	$95.967	$95.97	$95.95	$96.00
7 purchase totals =	$712.63		$769.8982	$769.91	$769.85	$770.00