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	$39.89	4.708%	$41.768	$41.77	$41.75	$41.80
Purchase #2	$137.53	11.168%	$152.8894	$152.89	$152.90	$152.90
Purchase #3	$197.66	10.705%	$218.8195	$218.82	$218.80	$218.80
Purchase #4	$35.78	13.598%	$40.6454	$40.65	$40.65	$40.60
Purchase #5	$126.46	8.613%	$137.352	$137.35	$137.35	$137.40
Purchase #6	$24.31	12.435%	$27.3329	$27.33	$27.35	$27.30
Purchase #7	$193.88	6.447%	$206.3794	$206.38	$206.40	$206.40
7 purchase totals =	$755.51		$825.1866	$825.19	$825.20	$825.20