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	$31.37	9.534%	$34.3608	$34.36	$34.35	$34.40
Purchase #2	$29.39	13.682%	$33.4111	$33.41	$33.40	$33.40
Purchase #3	$196.38	3.580%	$203.4104	$203.41	$203.40	$203.40
Purchase #4	$204.27	11.275%	$227.3014	$227.30	$227.30	$227.30
Purchase #5	$187.87	3.264%	$194.0021	$194.00	$194.00	$194.00
Purchase #6	$162.77	6.483%	$173.3224	$173.32	$173.30	$173.30
Purchase #7	$65.81	9.810%	$72.266	$72.27	$72.25	$72.30
7 purchase totals =	$877.86		$938.0742	$938.07	$938.00	$938.10