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	$62.72	3.232%	$64.7471	$64.75	$64.75	$64.70
Purchase #2	$100.46	12.263%	$112.7794	$112.78	$112.80	$112.80
Purchase #3	$78.63	13.768%	$89.4558	$89.46	$89.45	$89.50
Purchase #4	$130.47	3.393%	$134.8968	$134.90	$134.90	$134.90
Purchase #5	$100.67	12.464%	$113.2175	$113.22	$113.20	$113.20
Purchase #6	$89.42	11.658%	$99.8446	$99.84	$99.85	$99.80
Purchase #7	$39.64	4.698%	$41.5023	$41.50	$41.50	$41.50
7 purchase totals =	$602.01		$656.4435	$656.45	$656.45	$656.40