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	$74.78	5.503%	$78.8951	$78.90	$78.90	$78.90
Purchase #2	$76.95	11.255%	$85.6107	$85.61	$85.60	$85.60
Purchase #3	$71.99	9.227%	$78.6325	$78.63	$78.65	$78.60
Purchase #4	$31.69	8.570%	$34.4058	$34.41	$34.40	$34.40
Purchase #5	$233.99	13.175%	$264.8182	$264.82	$264.80	$264.80
Purchase #6	$111.68	13.112%	$126.3235	$126.32	$126.30	$126.30
Purchase #7	$170.48	10.205%	$187.8775	$187.88	$187.90	$187.90
7 purchase totals =	$771.56		$856.5633	$856.57	$856.55	$856.50