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	$38.61	5.695%	$40.8088	$40.81	$40.80	$40.80
Purchase #2	$37.68	12.480%	$42.3825	$42.38	$42.40	$42.40
Purchase #3	$132.86	7.361%	$142.6398	$142.64	$142.65	$142.60
Purchase #4	$74.48	11.300%	$82.8962	$82.90	$82.90	$82.90
Purchase #5	$151.76	11.789%	$169.651	$169.65	$169.65	$169.70
Purchase #6	$188.58	3.145%	$194.5108	$194.51	$194.50	$194.50
Purchase #7	$104.52	3.513%	$108.1918	$108.19	$108.20	$108.20
7 purchase totals =	$728.49		$781.0809	$781.08	$781.10	$781.10