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	$135.51	12.399%	$152.3119	$152.31	$152.30	$152.30
Purchase #2	$198.72	11.215%	$221.0064	$221.01	$221.00	$221.00
Purchase #3	$57.54	7.133%	$61.6443	$61.64	$61.65	$61.60
Purchase #4	$201.83	10.297%	$222.6124	$222.61	$222.60	$222.60
Purchase #5	$106.74	11.488%	$119.0023	$119.00	$119.00	$119.00
Purchase #6	$52.28	3.854%	$54.2949	$54.29	$54.30	$54.30
Purchase #7	$38.70	7.465%	$41.589	$41.59	$41.60	$41.60
7 purchase totals =	$791.32		$872.4612	$872.45	$872.45	$872.40