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	$159.32	13.187%	$180.3295	$180.33	$180.35	$180.30
Purchase #2	$90.46	5.477%	$95.4145	$95.41	$95.40	$95.40
Purchase #3	$191.65	4.615%	$200.4946	$200.49	$200.50	$200.50
Purchase #4	$75.29	12.821%	$84.9429	$84.94	$84.95	$84.90
Purchase #5	$33.90	8.529%	$36.7913	$36.79	$36.80	$36.80
Purchase #6	$57.34	3.411%	$59.2959	$59.30	$59.30	$59.30
Purchase #7	$13.59	13.181%	$15.3813	$15.38	$15.40	$15.40
7 purchase totals =	$621.55		$672.6500	$672.64	$672.70	$672.60