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	$172.89	6.774%	$184.6016	$184.60	$184.60	$184.60
Purchase #2	$127.36	11.181%	$141.6001	$141.60	$141.60	$141.60
Purchase #3	$151.90	4.793%	$159.1806	$159.18	$159.20	$159.20
Purchase #4	$186.65	3.354%	$192.9102	$192.91	$192.90	$192.90
Purchase #5	$145.53	3.229%	$150.2292	$150.23	$150.25	$150.20
Purchase #6	$80.46	9.759%	$88.3121	$88.31	$88.30	$88.30
Purchase #7	$161.67	7.606%	$173.9666	$173.97	$173.95	$174.00
7 purchase totals =	$1,026.46		$1,090.8004	$1,090.80	$1,090.80	$1,090.80