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	$198.37	12.156%	$222.4839	$222.48	$222.50	$222.50
Purchase #2	$74.92	11.314%	$83.3964	$83.40	$83.40	$83.40
Purchase #3	$245.38	3.452%	$253.8505	$253.85	$253.85	$253.90
Purchase #4	$186.36	13.476%	$211.4739	$211.47	$211.45	$211.50
Purchase #5	$240.69	3.682%	$249.5522	$249.55	$249.55	$249.60
Purchase #6	$174.63	4.833%	$183.0699	$183.07	$183.05	$183.10
Purchase #7	$164.87	8.837%	$179.4396	$179.44	$179.45	$179.40
7 purchase totals =	$1,285.22		$1,383.2664	$1,383.26	$1,383.25	$1,383.40