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	$248.98	10.668%	$275.5412	$275.54	$275.55	$275.50
Purchase #2	$43.37	5.838%	$45.9019	$45.90	$45.90	$45.90
Purchase #3	$32.48	10.652%	$35.9398	$35.94	$35.95	$35.90
Purchase #4	$45.39	4.488%	$47.4271	$47.43	$47.45	$47.40
Purchase #5	$182.89	4.400%	$190.9372	$190.94	$190.95	$190.90
Purchase #6	$130.97	5.363%	$137.9939	$137.99	$138.00	$138.00
Purchase #7	$31.64	4.505%	$33.0654	$33.07	$33.05	$33.10
7 purchase totals =	$715.72		$766.8065	$766.81	$766.85	$766.70