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	$106.32	10.178%	$117.1412	$117.14	$117.15	$117.10
Purchase #2	$44.82	13.645%	$50.9357	$50.94	$50.95	$50.90
Purchase #3	$163.78	10.276%	$180.61	$180.61	$180.60	$180.60
Purchase #4	$161.48	13.155%	$182.7227	$182.72	$182.70	$182.70
Purchase #5	$41.30	9.183%	$45.0926	$45.09	$45.10	$45.10
Purchase #6	$96.60	11.826%	$108.0239	$108.02	$108.00	$108.00
Purchase #7	$76.82	11.287%	$85.4907	$85.49	$85.50	$85.50
7 purchase totals =	$691.12		$770.0168	$770.01	$770.00	$769.90