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	$123.30	4.229%	$128.5144	$128.51	$128.50	$128.50
Purchase #2	$129.80	5.434%	$136.8533	$136.85	$136.85	$136.90
Purchase #3	$109.93	6.322%	$116.8798	$116.88	$116.90	$116.90
Purchase #4	$103.54	9.455%	$113.3297	$113.33	$113.35	$113.30
Purchase #5	$160.30	3.146%	$165.343	$165.34	$165.35	$165.30
Purchase #6	$221.35	5.853%	$234.3056	$234.31	$234.30	$234.30
Purchase #7	$171.47	12.720%	$193.281	$193.28	$193.30	$193.30
7 purchase totals =	$1,019.69		$1,088.5068	$1,088.50	$1,088.55	$1,088.50