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	$138.33	12.399%	$155.4815	$155.48	$155.50	$155.50
Purchase #2	$163.92	13.630%	$186.2623	$186.26	$186.25	$186.30
Purchase #3	$150.82	11.715%	$168.4886	$168.49	$168.50	$168.50
Purchase #4	$56.57	4.867%	$59.3233	$59.32	$59.30	$59.30
Purchase #5	$124.87	5.739%	$132.0363	$132.04	$132.05	$132.00
Purchase #6	$95.76	3.292%	$98.9124	$98.91	$98.90	$98.90
Purchase #7	$36.77	5.192%	$38.6791	$38.68	$38.70	$38.70
7 purchase totals =	$767.04		$839.1835	$839.18	$839.20	$839.20