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	$123.58	11.110%	$137.3097	$137.31	$137.30	$137.30
Purchase #2	$186.69	6.536%	$198.8921	$198.89	$198.90	$198.90
Purchase #3	$18.27	5.865%	$19.3415	$19.34	$19.35	$19.30
Purchase #4	$41.98	8.547%	$45.568	$45.57	$45.55	$45.60
Purchase #5	$204.70	4.111%	$213.1152	$213.12	$213.10	$213.10
Purchase #6	$160.32	6.760%	$171.1576	$171.16	$171.15	$171.20
Purchase #7	$42.69	6.782%	$45.5852	$45.59	$45.60	$45.60
7 purchase totals =	$778.23		$830.9693	$830.98	$830.95	$831.00