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	$49.35	11.332%	$54.9423	$54.94	$54.95	$54.90
Purchase #2	$147.92	12.220%	$165.9958	$166.00	$166.00	$166.00
Purchase #3	$234.79	4.535%	$245.4377	$245.44	$245.45	$245.40
Purchase #4	$225.79	3.316%	$233.2772	$233.28	$233.30	$233.30
Purchase #5	$162.57	4.339%	$169.6239	$169.62	$169.60	$169.60
Purchase #6	$78.67	6.168%	$83.5224	$83.52	$83.50	$83.50
Purchase #7	$173.75	9.864%	$190.8887	$190.89	$190.90	$190.90
7 purchase totals =	$1,072.84		$1,143.6880	$1,143.69	$1,143.70	$1,143.60