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	$82.68	9.638%	$90.6487	$90.65	$90.65	$90.60
Purchase #2	$105.91	4.842%	$111.0382	$111.04	$111.05	$111.00
Purchase #3	$205.95	10.581%	$227.7416	$227.74	$227.75	$227.70
Purchase #4	$63.83	12.690%	$71.93	$71.93	$71.95	$71.90
Purchase #5	$199.77	5.520%	$210.7973	$210.80	$210.80	$210.80
Purchase #6	$31.88	9.661%	$34.9599	$34.96	$34.95	$35.00
Purchase #7	$188.33	4.477%	$196.7615	$196.76	$196.75	$196.80
7 purchase totals =	$878.35		$943.8772	$943.88	$943.90	$943.80