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	$231.31	6.318%	$245.9242	$245.92	$245.90	$245.90
Purchase #2	$205.51	13.754%	$233.7758	$233.78	$233.80	$233.80
Purchase #3	$169.98	7.337%	$182.4514	$182.45	$182.45	$182.50
Purchase #4	$152.30	9.235%	$166.3649	$166.36	$166.35	$166.40
Purchase #5	$31.90	10.254%	$35.171	$35.17	$35.15	$35.20
Purchase #6	$173.82	6.763%	$185.5754	$185.58	$185.60	$185.60
Purchase #7	$238.37	12.578%	$268.3522	$268.35	$268.35	$268.40
7 purchase totals =	$1,203.19		$1,317.6149	$1,317.61	$1,317.60	$1,317.80