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	$58.51	9.315%	$63.9602	$63.96	$63.95	$64.00
Purchase #2	$238.47	10.839%	$264.3178	$264.32	$264.30	$264.30
Purchase #3	$148.39	11.290%	$165.1432	$165.14	$165.15	$165.10
Purchase #4	$90.52	7.261%	$97.0927	$97.09	$97.10	$97.10
Purchase #5	$168.96	12.542%	$190.151	$190.15	$190.15	$190.20
Purchase #6	$37.48	3.613%	$38.8342	$38.83	$38.85	$38.80
Purchase #7	$35.87	3.284%	$37.048	$37.05	$37.05	$37.00
7 purchase totals =	$778.20		$856.5471	$856.54	$856.55	$856.50