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	$83.38	7.426%	$89.5718	$89.57	$89.55	$89.60
Purchase #2	$184.86	11.236%	$205.6309	$205.63	$205.65	$205.60
Purchase #3	$250.53	11.485%	$279.3034	$279.30	$279.30	$279.30
Purchase #4	$148.80	13.233%	$168.4907	$168.49	$168.50	$168.50
Purchase #5	$97.77	11.510%	$109.0233	$109.02	$109.00	$109.00
Purchase #6	$152.57	12.698%	$171.9433	$171.94	$171.95	$171.90
Purchase #7	$60.46	3.185%	$62.3857	$62.39	$62.40	$62.40
7 purchase totals =	$978.37		$1,086.3491	$1,086.34	$1,086.35	$1,086.30