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	$96.83	3.161%	$99.8908	$99.89	$99.90	$99.90
Purchase #2	$38.91	12.829%	$43.9018	$43.90	$43.90	$43.90
Purchase #3	$173.70	10.116%	$191.2715	$191.27	$191.25	$191.30
Purchase #4	$198.99	13.441%	$225.7362	$225.74	$225.75	$225.70
Purchase #5	$23.55	3.430%	$24.3578	$24.36	$24.35	$24.40
Purchase #6	$187.48	13.777%	$213.3091	$213.31	$213.30	$213.30
Purchase #7	$214.58	11.318%	$238.8662	$238.87	$238.85	$238.90
7 purchase totals =	$934.04		$1,037.3334	$1,037.34	$1,037.30	$1,037.40