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	$86.46	4.827%	$90.6334	$90.63	$90.65	$90.60
Purchase #2	$97.30	3.214%	$100.4272	$100.43	$100.45	$100.40
Purchase #3	$136.72	9.835%	$150.1664	$150.17	$150.15	$150.20
Purchase #4	$218.88	8.605%	$237.7146	$237.71	$237.70	$237.70
Purchase #5	$117.34	8.515%	$127.3315	$127.33	$127.35	$127.30
Purchase #6	$80.81	12.611%	$91.0009	$91.00	$91.00	$91.00
Purchase #7	$100.40	7.435%	$107.8647	$107.86	$107.85	$107.90
7 purchase totals =	$837.91		$905.1387	$905.13	$905.15	$905.10