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	$18.32	11.414%	$20.411	$20.41	$20.40	$20.40
Purchase #2	$182.27	5.345%	$192.0123	$192.01	$192.00	$192.00
Purchase #3	$71.89	13.798%	$81.8094	$81.81	$81.80	$81.80
Purchase #4	$194.25	12.476%	$218.4846	$218.48	$218.50	$218.50
Purchase #5	$37.54	10.723%	$41.5654	$41.57	$41.55	$41.60
Purchase #6	$39.45	8.614%	$42.8482	$42.85	$42.85	$42.80
Purchase #7	$85.36	12.657%	$96.164	$96.16	$96.15	$96.20
7 purchase totals =	$629.08		$693.2949	$693.29	$693.25	$693.30