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	$133.33	8.336%	$144.4444	$144.44	$144.45	$144.40
Purchase #2	$101.90	5.816%	$107.8265	$107.83	$107.85	$107.80
Purchase #3	$141.96	12.558%	$159.7873	$159.79	$159.80	$159.80
Purchase #4	$159.99	9.650%	$175.429	$175.43	$175.45	$175.40
Purchase #5	$67.60	7.238%	$72.4929	$72.49	$72.50	$72.50
Purchase #6	$59.59	5.108%	$62.6339	$62.63	$62.65	$62.60
Purchase #7	$229.97	3.732%	$238.5525	$238.55	$238.55	$238.60
7 purchase totals =	$894.34		$961.1665	$961.16	$961.25	$961.10