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	$55.44	10.583%	$61.3072	$61.31	$61.30	$61.30
Purchase #2	$186.31	12.354%	$209.3267	$209.33	$209.35	$209.30
Purchase #3	$145.48	10.440%	$160.6681	$160.67	$160.65	$160.70
Purchase #4	$215.83	12.410%	$242.6145	$242.61	$242.60	$242.60
Purchase #5	$45.86	6.855%	$49.0037	$49.00	$49.00	$49.00
Purchase #6	$33.77	7.299%	$36.2349	$36.23	$36.25	$36.20
Purchase #7	$78.70	8.414%	$85.3218	$85.32	$85.30	$85.30
7 purchase totals =	$761.39		$844.4769	$844.47	$844.45	$844.40