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	$246.93	9.325%	$269.9562	$269.96	$269.95	$270.00
Purchase #2	$40.76	4.189%	$42.4674	$42.47	$42.45	$42.50
Purchase #3	$150.61	9.196%	$164.4601	$164.46	$164.45	$164.50
Purchase #4	$95.89	4.742%	$100.4371	$100.44	$100.45	$100.40
Purchase #5	$86.41	8.274%	$93.5596	$93.56	$93.55	$93.60
Purchase #6	$104.77	9.828%	$115.0668	$115.07	$115.05	$115.10
Purchase #7	$44.77	12.303%	$50.2781	$50.28	$50.30	$50.30
7 purchase totals =	$770.14		$836.2253	$836.24	$836.20	$836.40