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	$131.39	6.510%	$139.9435	$139.94	$139.95	$139.90
Purchase #2	$72.36	3.293%	$74.7428	$74.74	$74.75	$74.70
Purchase #3	$224.75	3.808%	$233.3085	$233.31	$233.30	$233.30
Purchase #4	$75.93	9.162%	$82.8867	$82.89	$82.90	$82.90
Purchase #5	$56.92	3.790%	$59.0773	$59.08	$59.10	$59.10
Purchase #6	$58.64	4.577%	$61.324	$61.32	$61.30	$61.30
Purchase #7	$16.94	13.219%	$19.1793	$19.18	$19.20	$19.20
7 purchase totals =	$636.93		$670.4621	$670.46	$670.50	$670.40