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	$82.41	11.493%	$91.8814	$91.88	$91.90	$91.90
Purchase #2	$97.32	11.586%	$108.5955	$108.60	$108.60	$108.60
Purchase #3	$219.99	10.419%	$242.9108	$242.91	$242.90	$242.90
Purchase #4	$177.31	4.478%	$185.2499	$185.25	$185.25	$185.20
Purchase #5	$135.39	4.259%	$141.1563	$141.16	$141.15	$141.20
Purchase #6	$27.89	4.765%	$29.219	$29.22	$29.20	$29.20
Purchase #7	$230.89	13.821%	$262.8013	$262.80	$262.80	$262.80
7 purchase totals =	$971.20		$1,061.8142	$1,061.82	$1,061.80	$1,061.80