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	$181.96	12.573%	$204.8378	$204.84	$204.85	$204.80
Purchase #2	$212.63	12.308%	$238.8005	$238.80	$238.80	$238.80
Purchase #3	$142.52	6.168%	$151.3106	$151.31	$151.30	$151.30
Purchase #4	$193.80	3.504%	$200.5908	$200.59	$200.60	$200.60
Purchase #5	$109.50	9.486%	$119.8872	$119.89	$119.90	$119.90
Purchase #6	$72.52	6.593%	$77.3012	$77.30	$77.30	$77.30
Purchase #7	$35.81	11.811%	$40.0395	$40.04	$40.05	$40.00
7 purchase totals =	$948.74		$1,032.7676	$1,032.77	$1,032.80	$1,032.70