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	$84.78	8.652%	$92.1152	$92.12	$92.10	$92.10
Purchase #2	$33.59	5.153%	$35.3209	$35.32	$35.30	$35.30
Purchase #3	$234.71	7.822%	$253.069	$253.07	$253.05	$253.10
Purchase #4	$122.49	7.578%	$131.7723	$131.77	$131.75	$131.80
Purchase #5	$173.38	13.524%	$196.8279	$196.83	$196.85	$196.80
Purchase #6	$209.69	3.201%	$216.4022	$216.40	$216.40	$216.40
Purchase #7	$52.97	4.570%	$55.3907	$55.39	$55.40	$55.40
7 purchase totals =	$911.61		$980.8982	$980.90	$980.85	$980.90