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	$70.47	3.321%	$72.8103	$72.81	$72.80	$72.80
Purchase #2	$72.34	7.704%	$77.9131	$77.91	$77.90	$77.90
Purchase #3	$47.27	11.265%	$52.595	$52.60	$52.60	$52.60
Purchase #4	$51.46	10.309%	$56.765	$56.77	$56.75	$56.80
Purchase #5	$41.57	12.441%	$46.7417	$46.74	$46.75	$46.70
Purchase #6	$188.89	12.807%	$213.0811	$213.08	$213.10	$213.10
Purchase #7	$124.56	9.496%	$136.3882	$136.39	$136.40	$136.40
7 purchase totals =	$596.56		$656.2944	$656.30	$656.30	$656.30