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	$18.30	13.809%	$20.827	$20.83	$20.85	$20.80
Purchase #2	$170.94	10.477%	$188.8494	$188.85	$188.85	$188.80
Purchase #3	$163.31	11.250%	$181.6824	$181.68	$181.70	$181.70
Purchase #4	$37.73	7.688%	$40.6307	$40.63	$40.65	$40.60
Purchase #5	$62.88	12.154%	$70.5224	$70.52	$70.50	$70.50
Purchase #6	$110.49	7.365%	$118.6276	$118.63	$118.65	$118.60
Purchase #7	$99.46	5.508%	$104.9383	$104.94	$104.95	$104.90
7 purchase totals =	$663.11		$726.0778	$726.08	$726.15	$725.90