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	$115.90	9.866%	$127.3347	$127.33	$127.35	$127.30
Purchase #2	$21.57	12.535%	$24.2738	$24.27	$24.25	$24.30
Purchase #3	$34.87	11.626%	$38.924	$38.92	$38.90	$38.90
Purchase #4	$132.35	13.251%	$149.8877	$149.89	$149.90	$149.90
Purchase #5	$178.90	8.629%	$194.3373	$194.34	$194.35	$194.30
Purchase #6	$133.91	4.819%	$140.3631	$140.36	$140.35	$140.40
Purchase #7	$195.33	10.180%	$215.2146	$215.21	$215.20	$215.20
7 purchase totals =	$812.83		$890.3352	$890.32	$890.30	$890.30