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	$116.45	9.524%	$127.5407	$127.54	$127.55	$127.50
Purchase #2	$134.38	12.196%	$150.769	$150.77	$150.75	$150.80
Purchase #3	$202.58	9.399%	$221.6205	$221.62	$221.60	$221.60
Purchase #4	$27.80	11.143%	$30.8978	$30.90	$30.90	$30.90
Purchase #5	$117.52	5.751%	$124.2786	$124.28	$124.30	$124.30
Purchase #6	$208.27	6.629%	$222.0762	$222.08	$222.10	$222.10
Purchase #7	$62.95	7.731%	$67.8167	$67.82	$67.80	$67.80
7 purchase totals =	$869.95		$944.9995	$945.01	$945.00	$945.00