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	$75.41	6.780%	$80.5228	$80.52	$80.50	$80.50
Purchase #2	$219.82	11.514%	$245.1301	$245.13	$245.15	$245.10
Purchase #3	$116.82	5.162%	$122.8502	$122.85	$122.85	$122.90
Purchase #4	$114.49	11.364%	$127.5006	$127.50	$127.50	$127.50
Purchase #5	$232.70	6.579%	$248.0093	$248.01	$248.00	$248.00
Purchase #6	$102.86	10.264%	$113.4176	$113.42	$113.40	$113.40
Purchase #7	$88.50	3.834%	$91.8931	$91.89	$91.90	$91.90
7 purchase totals =	$950.60		$1,029.3237	$1,029.32	$1,029.30	$1,029.30