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	$199.67	5.589%	$210.8296	$210.83	$210.85	$210.80
Purchase #2	$220.56	11.433%	$245.7766	$245.78	$245.80	$245.80
Purchase #3	$213.85	13.338%	$242.3733	$242.37	$242.35	$242.40
Purchase #4	$81.63	11.355%	$90.8991	$90.90	$90.90	$90.90
Purchase #5	$167.97	4.663%	$175.8024	$175.80	$175.80	$175.80
Purchase #6	$186.55	11.778%	$208.5219	$208.52	$208.50	$208.50
Purchase #7	$87.77	13.218%	$99.3714	$99.37	$99.35	$99.40
7 purchase totals =	$1,158.00		$1,273.5743	$1,273.57	$1,273.55	$1,273.60