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	$31.61	6.862%	$33.7791	$33.78	$33.80	$33.80
Purchase #2	$37.48	11.718%	$41.8719	$41.87	$41.85	$41.90
Purchase #3	$138.77	5.823%	$146.8506	$146.85	$146.85	$146.90
Purchase #4	$137.83	4.691%	$144.2956	$144.30	$144.30	$144.30
Purchase #5	$141.30	4.503%	$147.6627	$147.66	$147.65	$147.70
Purchase #6	$208.46	7.174%	$223.4149	$223.41	$223.40	$223.40
Purchase #7	$116.32	6.421%	$123.7889	$123.79	$123.80	$123.80
7 purchase totals =	$811.77		$861.6637	$861.66	$861.65	$861.80