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	$38.37	10.361%	$42.3455	$42.35	$42.35	$42.30
Purchase #2	$130.97	8.739%	$142.4155	$142.42	$142.40	$142.40
Purchase #3	$72.31	9.520%	$79.1939	$79.19	$79.20	$79.20
Purchase #4	$86.53	7.393%	$92.9272	$92.93	$92.95	$92.90
Purchase #5	$229.59	3.447%	$237.504	$237.50	$237.50	$237.50
Purchase #6	$83.37	3.370%	$86.1796	$86.18	$86.20	$86.20
Purchase #7	$109.64	12.762%	$123.6323	$123.63	$123.65	$123.60
7 purchase totals =	$750.78		$804.1980	$804.20	$804.25	$804.10