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	$78.59	12.587%	$88.4821	$88.48	$88.50	$88.50
Purchase #2	$178.53	6.240%	$189.6703	$189.67	$189.65	$189.70
Purchase #3	$210.87	5.495%	$222.4573	$222.46	$222.45	$222.50
Purchase #4	$218.53	9.858%	$240.0727	$240.07	$240.05	$240.10
Purchase #5	$14.40	10.754%	$15.9486	$15.95	$15.95	$15.90
Purchase #6	$190.83	3.213%	$196.9614	$196.96	$196.95	$197.00
Purchase #7	$17.59	4.482%	$18.3784	$18.38	$18.40	$18.40
7 purchase totals =	$909.34		$971.9708	$971.97	$971.95	$972.10