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	$126.92	10.746%	$140.5588	$140.56	$140.55	$140.60
Purchase #2	$99.70	3.354%	$103.0439	$103.04	$103.05	$103.00
Purchase #3	$245.36	10.785%	$271.8221	$271.82	$271.80	$271.80
Purchase #4	$210.63	11.449%	$234.745	$234.75	$234.75	$234.70
Purchase #5	$12.88	4.631%	$13.4765	$13.48	$13.50	$13.50
Purchase #6	$78.61	8.577%	$85.3524	$85.35	$85.35	$85.40
Purchase #7	$143.44	7.622%	$154.373	$154.37	$154.35	$154.40
7 purchase totals =	$917.54		$1,003.3717	$1,003.37	$1,003.35	$1,003.40