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	$29.75	4.335%	$31.0397	$31.04	$31.05	$31.00
Purchase #2	$96.42	3.599%	$99.8902	$99.89	$99.90	$99.90
Purchase #3	$53.28	12.206%	$59.7834	$59.78	$59.80	$59.80
Purchase #4	$162.32	5.376%	$171.0463	$171.05	$171.05	$171.00
Purchase #5	$230.48	12.373%	$258.9973	$259.00	$259.00	$259.00
Purchase #6	$59.85	5.121%	$62.9149	$62.91	$62.90	$62.90
Purchase #7	$89.68	10.402%	$99.0085	$99.01	$99.00	$99.00
7 purchase totals =	$721.78		$782.6803	$782.68	$782.70	$782.60