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	$131.83	10.218%	$145.3004	$145.30	$145.30	$145.30
Purchase #2	$44.97	10.132%	$49.5264	$49.53	$49.55	$49.50
Purchase #3	$145.39	3.822%	$150.9468	$150.95	$150.95	$150.90
Purchase #4	$82.37	13.127%	$93.1827	$93.18	$93.20	$93.20
Purchase #5	$250.55	13.555%	$284.5121	$284.51	$284.50	$284.50
Purchase #6	$97.89	4.720%	$102.5104	$102.51	$102.50	$102.50
Purchase #7	$74.75	5.590%	$78.9285	$78.93	$78.95	$78.90
7 purchase totals =	$827.75		$904.9073	$904.91	$904.95	$904.80