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	$137.63	12.329%	$154.5984	$154.60	$154.60	$154.60
Purchase #2	$240.32	7.744%	$258.9304	$258.93	$258.95	$258.90
Purchase #3	$7.40	6.653%	$7.8923	$7.89	$7.90	$7.90
Purchase #4	$233.45	5.479%	$246.2407	$246.24	$246.25	$246.20
Purchase #5	$124.72	10.201%	$137.4427	$137.44	$137.45	$137.40
Purchase #6	$236.77	12.170%	$265.5849	$265.58	$265.60	$265.60
Purchase #7	$31.27	12.833%	$35.2829	$35.28	$35.30	$35.30
7 purchase totals =	$1,011.56		$1,105.9723	$1,105.96	$1,106.05	$1,105.90