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	$78.90	12.218%	$88.54	$88.54	$88.55	$88.50
Purchase #2	$37.55	11.779%	$41.973	$41.97	$41.95	$42.00
Purchase #3	$102.70	10.698%	$113.6868	$113.69	$113.70	$113.70
Purchase #4	$209.42	6.143%	$222.2847	$222.28	$222.30	$222.30
Purchase #5	$198.98	5.186%	$209.2991	$209.30	$209.30	$209.30
Purchase #6	$132.91	7.653%	$143.0816	$143.08	$143.10	$143.10
Purchase #7	$175.25	13.728%	$199.3083	$199.31	$199.30	$199.30
7 purchase totals =	$935.71		$1,018.1735	$1,018.17	$1,018.20	$1,018.20