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	$36.36	11.128%	$40.4061	$40.41	$40.40	$40.40
Purchase #2	$154.95	8.735%	$168.4849	$168.48	$168.50	$168.50
Purchase #3	$141.76	9.765%	$155.6029	$155.60	$155.60	$155.60
Purchase #4	$154.29	11.676%	$172.3049	$172.30	$172.30	$172.30
Purchase #5	$225.67	5.611%	$238.3323	$238.33	$238.35	$238.30
Purchase #6	$151.30	6.862%	$161.6822	$161.68	$161.70	$161.70
Purchase #7	$68.87	6.715%	$73.4946	$73.49	$73.50	$73.50
7 purchase totals =	$933.20		$1,010.3079	$1,010.29	$1,010.35	$1,010.30