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	$32.73	13.138%	$37.0301	$37.03	$37.05	$37.00
Purchase #2	$32.96	6.436%	$35.0813	$35.08	$35.10	$35.10
Purchase #3	$157.31	11.264%	$175.0294	$175.03	$175.05	$175.00
Purchase #4	$226.33	3.413%	$234.0546	$234.05	$234.05	$234.10
Purchase #5	$131.87	12.488%	$148.3379	$148.34	$148.35	$148.30
Purchase #6	$137.41	5.224%	$144.5883	$144.59	$144.60	$144.60
Purchase #7	$142.49	11.573%	$158.9804	$158.98	$159.00	$159.00
7 purchase totals =	$861.10		$933.1020	$933.10	$933.20	$933.10