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	$139.41	11.779%	$155.8311	$155.83	$155.85	$155.80
Purchase #2	$223.50	6.562%	$238.1661	$238.17	$238.15	$238.20
Purchase #3	$175.79	9.280%	$192.1033	$192.10	$192.10	$192.10
Purchase #4	$56.85	9.269%	$62.1194	$62.12	$62.10	$62.10
Purchase #5	$19.58	11.651%	$21.8613	$21.86	$21.85	$21.90
Purchase #6	$143.89	11.420%	$160.3222	$160.32	$160.30	$160.30
Purchase #7	$149.56	6.677%	$159.5461	$159.55	$159.55	$159.50
7 purchase totals =	$908.58		$989.9495	$989.95	$989.90	$989.90