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	$92.52	12.758%	$104.3237	$104.32	$104.30	$104.30
Purchase #2	$227.37	3.708%	$235.8009	$235.80	$235.80	$235.80
Purchase #3	$127.35	7.663%	$137.1088	$137.11	$137.10	$137.10
Purchase #4	$117.45	5.399%	$123.7911	$123.79	$123.80	$123.80
Purchase #5	$221.69	9.650%	$243.0831	$243.08	$243.10	$243.10
Purchase #6	$65.78	9.216%	$71.8423	$71.84	$71.85	$71.80
Purchase #7	$145.69	6.332%	$154.9151	$154.92	$154.90	$154.90
7 purchase totals =	$997.85		$1,070.8650	$1,070.86	$1,070.85	$1,070.80