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	$78.34	6.422%	$83.371	$83.37	$83.35	$83.40
Purchase #2	$101.90	9.692%	$111.7761	$111.78	$111.80	$111.80
Purchase #3	$29.66	5.216%	$31.2071	$31.21	$31.20	$31.20
Purchase #4	$174.51	8.547%	$189.4254	$189.43	$189.45	$189.40
Purchase #5	$93.99	5.245%	$98.9198	$98.92	$98.90	$98.90
Purchase #6	$250.55	6.271%	$266.262	$266.26	$266.25	$266.30
Purchase #7	$208.94	6.711%	$222.962	$222.96	$222.95	$223.00
7 purchase totals =	$937.89		$1,003.9234	$1,003.93	$1,003.90	$1,004.00