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	$35.38	6.836%	$37.7986	$37.80	$37.80	$37.80
Purchase #2	$131.64	6.855%	$140.6639	$140.66	$140.65	$140.70
Purchase #3	$154.78	5.229%	$162.8734	$162.87	$162.85	$162.90
Purchase #4	$146.47	4.390%	$152.9	$152.90	$152.90	$152.90
Purchase #5	$196.33	4.647%	$205.4535	$205.45	$205.45	$205.50
Purchase #6	$164.56	6.277%	$174.8894	$174.89	$174.90	$174.90
Purchase #7	$42.25	10.816%	$46.8198	$46.82	$46.80	$46.80
7 purchase totals =	$871.41		$921.3986	$921.39	$921.35	$921.50