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	$90.75	13.517%	$103.0167	$103.02	$103.00	$103.00
Purchase #2	$135.87	13.780%	$154.5929	$154.59	$154.60	$154.60
Purchase #3	$160.75	12.831%	$181.3758	$181.38	$181.40	$181.40
Purchase #4	$89.59	8.692%	$97.3772	$97.38	$97.40	$97.40
Purchase #5	$163.36	11.508%	$182.1595	$182.16	$182.15	$182.20
Purchase #6	$89.85	13.119%	$101.6374	$101.64	$101.65	$101.60
Purchase #7	$245.55	11.437%	$273.6336	$273.63	$273.65	$273.60
7 purchase totals =	$975.72		$1,093.7931	$1,093.80	$1,093.85	$1,093.80