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	$67.69	6.856%	$72.3308	$72.33	$72.35	$72.30
Purchase #2	$59.68	9.384%	$65.2804	$65.28	$65.30	$65.30
Purchase #3	$124.44	10.505%	$137.5124	$137.51	$137.50	$137.50
Purchase #4	$37.87	11.284%	$42.1433	$42.14	$42.15	$42.10
Purchase #5	$214.57	10.403%	$236.8917	$236.89	$236.90	$236.90
Purchase #6	$72.28	11.557%	$80.6334	$80.63	$80.65	$80.60
Purchase #7	$22.26	3.288%	$22.9919	$22.99	$23.00	$23.00
7 purchase totals =	$598.79		$657.7839	$657.77	$657.85	$657.70