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	$241.86	11.667%	$270.0778	$270.08	$270.10	$270.10
Purchase #2	$239.48	3.227%	$247.208	$247.21	$247.20	$247.20
Purchase #3	$206.72	5.728%	$218.5609	$218.56	$218.55	$218.60
Purchase #4	$142.91	3.792%	$148.3291	$148.33	$148.35	$148.30
Purchase #5	$111.36	6.603%	$118.7131	$118.71	$118.70	$118.70
Purchase #6	$18.34	11.424%	$20.4352	$20.44	$20.45	$20.40
Purchase #7	$51.69	11.503%	$57.6359	$57.64	$57.65	$57.60
7 purchase totals =	$1,012.36		$1,080.9600	$1,080.97	$1,081.00	$1,080.90