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	$58.97	9.617%	$64.6411	$64.64	$64.65	$64.60
Purchase #2	$31.40	11.284%	$34.9432	$34.94	$34.95	$34.90
Purchase #3	$31.76	12.560%	$35.7491	$35.75	$35.75	$35.70
Purchase #4	$236.57	9.655%	$259.4108	$259.41	$259.40	$259.40
Purchase #5	$74.68	10.676%	$82.6528	$82.65	$82.65	$82.70
Purchase #6	$55.80	9.696%	$61.2104	$61.21	$61.20	$61.20
Purchase #7	$122.71	4.679%	$128.4516	$128.45	$128.45	$128.50
7 purchase totals =	$611.89		$667.0590	$667.05	$667.05	$667.00