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	$109.40	12.457%	$123.028	$123.03	$123.05	$123.00
Purchase #2	$202.35	11.443%	$225.5049	$225.50	$225.50	$225.50
Purchase #3	$37.25	5.787%	$39.4057	$39.41	$39.40	$39.40
Purchase #4	$140.69	11.496%	$156.8637	$156.86	$156.85	$156.90
Purchase #5	$221.81	4.201%	$231.1282	$231.13	$231.15	$231.10
Purchase #6	$222.81	7.130%	$238.6964	$238.70	$238.70	$238.70
Purchase #7	$221.79	11.139%	$246.4952	$246.50	$246.50	$246.50
7 purchase totals =	$1,156.10		$1,261.1221	$1,261.13	$1,261.15	$1,261.10