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	$188.99	13.345%	$214.2107	$214.21	$214.20	$214.20
Purchase #2	$102.62	10.768%	$113.6701	$113.67	$113.65	$113.70
Purchase #3	$48.37	4.597%	$50.5936	$50.59	$50.60	$50.60
Purchase #4	$115.74	13.582%	$131.4598	$131.46	$131.45	$131.50
Purchase #5	$56.98	4.218%	$59.3834	$59.38	$59.40	$59.40
Purchase #6	$159.60	12.712%	$179.8884	$179.89	$179.90	$179.90
Purchase #7	$122.78	6.275%	$130.4844	$130.48	$130.50	$130.50
7 purchase totals =	$795.08		$879.6904	$879.68	$879.70	$879.80