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	$180.27	4.614%	$188.5877	$188.59	$188.60	$188.60
Purchase #2	$53.82	11.180%	$59.8371	$59.84	$59.85	$59.80
Purchase #3	$188.51	4.392%	$196.7894	$196.79	$196.80	$196.80
Purchase #4	$146.97	7.460%	$157.934	$157.93	$157.95	$157.90
Purchase #5	$28.36	9.305%	$30.9989	$31.00	$31.00	$31.00
Purchase #6	$236.67	10.403%	$261.2908	$261.29	$261.30	$261.30
Purchase #7	$86.30	3.555%	$89.368	$89.37	$89.35	$89.40
7 purchase totals =	$920.90		$984.8059	$984.81	$984.85	$984.80