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	$76.39	12.212%	$85.7187	$85.72	$85.70	$85.70
Purchase #2	$232.83	11.411%	$259.3982	$259.40	$259.40	$259.40
Purchase #3	$239.61	8.796%	$260.6861	$260.69	$260.70	$260.70
Purchase #4	$185.50	5.815%	$196.2868	$196.29	$196.30	$196.30
Purchase #5	$197.99	12.727%	$223.1882	$223.19	$223.20	$223.20
Purchase #6	$169.56	9.766%	$186.1192	$186.12	$186.10	$186.10
Purchase #7	$80.72	11.853%	$90.2877	$90.29	$90.30	$90.30
7 purchase totals =	$1,182.60		$1,301.6849	$1,301.70	$1,301.70	$1,301.70