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	$142.85	3.802%	$148.2812	$148.28	$148.30	$148.30
Purchase #2	$20.93	12.455%	$23.5368	$23.54	$23.55	$23.50
Purchase #3	$83.52	10.628%	$92.3965	$92.40	$92.40	$92.40
Purchase #4	$161.66	8.405%	$175.2475	$175.25	$175.25	$175.20
Purchase #5	$30.48	10.850%	$33.7871	$33.79	$33.80	$33.80
Purchase #6	$41.83	8.861%	$45.5366	$45.54	$45.55	$45.50
Purchase #7	$64.57	10.860%	$71.5823	$71.58	$71.60	$71.60
7 purchase totals =	$545.84		$590.3680	$590.38	$590.45	$590.30