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	$17.88	3.377%	$18.4838	$18.48	$18.50	$18.50
Purchase #2	$221.27	9.504%	$242.2995	$242.30	$242.30	$242.30
Purchase #3	$171.45	5.549%	$180.9638	$180.96	$180.95	$181.00
Purchase #4	$80.99	5.311%	$85.2914	$85.29	$85.30	$85.30
Purchase #5	$119.63	9.849%	$131.4124	$131.41	$131.40	$131.40
Purchase #6	$127.73	3.195%	$131.811	$131.81	$131.80	$131.80
Purchase #7	$167.63	5.113%	$176.2009	$176.20	$176.20	$176.20
7 purchase totals =	$906.58		$966.4628	$966.45	$966.45	$966.50