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	$38.53	10.414%	$42.5425	$42.54	$42.55	$42.50
Purchase #2	$83.83	12.523%	$94.328	$94.33	$94.35	$94.30
Purchase #3	$215.57	10.659%	$238.5476	$238.55	$238.55	$238.50
Purchase #4	$116.34	10.291%	$128.3125	$128.31	$128.30	$128.30
Purchase #5	$216.77	5.825%	$229.3969	$229.40	$229.40	$229.40
Purchase #6	$95.80	10.727%	$106.0765	$106.08	$106.10	$106.10
Purchase #7	$240.27	7.379%	$257.9995	$258.00	$258.00	$258.00
7 purchase totals =	$1,007.11		$1,097.2035	$1,097.21	$1,097.25	$1,097.10