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	$123.48	11.358%	$137.5049	$137.50	$137.50	$137.50
Purchase #2	$109.38	6.187%	$116.1473	$116.15	$116.15	$116.10
Purchase #3	$63.72	12.111%	$71.4371	$71.44	$71.45	$71.40
Purchase #4	$176.35	7.456%	$189.4987	$189.50	$189.50	$189.50
Purchase #5	$68.78	13.270%	$77.9071	$77.91	$77.90	$77.90
Purchase #6	$176.79	6.190%	$187.7333	$187.73	$187.75	$187.70
Purchase #7	$189.55	5.618%	$200.1989	$200.20	$200.20	$200.20
7 purchase totals =	$908.05		$980.4273	$980.43	$980.45	$980.30