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	$229.43	11.568%	$255.9705	$255.97	$255.95	$256.00
Purchase #2	$131.70	3.499%	$136.3082	$136.31	$136.30	$136.30
Purchase #3	$37.64	11.868%	$42.1071	$42.11	$42.10	$42.10
Purchase #4	$149.98	3.555%	$155.3118	$155.31	$155.30	$155.30
Purchase #5	$171.69	3.576%	$177.8296	$177.83	$177.85	$177.80
Purchase #6	$100.52	12.499%	$113.084	$113.08	$113.10	$113.10
Purchase #7	$119.84	6.305%	$127.3959	$127.40	$127.40	$127.40
7 purchase totals =	$940.80		$1,008.0071	$1,008.01	$1,008.00	$1,008.00