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	$94.76	7.871%	$102.2186	$102.22	$102.20	$102.20
Purchase #2	$169.86	10.261%	$187.2893	$187.29	$187.30	$187.30
Purchase #3	$113.29	12.619%	$127.5861	$127.59	$127.60	$127.60
Purchase #4	$82.28	13.848%	$93.6741	$93.67	$93.65	$93.70
Purchase #5	$59.27	3.219%	$61.1779	$61.18	$61.20	$61.20
Purchase #6	$169.51	13.459%	$192.3244	$192.32	$192.30	$192.30
Purchase #7	$127.46	11.328%	$141.8987	$141.90	$141.90	$141.90
7 purchase totals =	$816.43		$906.1691	$906.17	$906.15	$906.20