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	$33.85	4.671%	$35.4311	$35.43	$35.45	$35.40
Purchase #2	$221.99	5.583%	$234.3837	$234.38	$234.40	$234.40
Purchase #3	$149.59	12.616%	$168.4623	$168.46	$168.45	$168.50
Purchase #4	$7.64	11.205%	$8.4961	$8.50	$8.50	$8.50
Purchase #5	$38.28	11.412%	$42.6485	$42.65	$42.65	$42.60
Purchase #6	$29.61	11.224%	$32.9334	$32.93	$32.95	$32.90
Purchase #7	$7.53	4.589%	$7.8756	$7.88	$7.90	$7.90
7 purchase totals =	$488.49		$530.2307	$530.23	$530.30	$530.20