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	$38.86	9.318%	$42.481	$42.48	$42.50	$42.50
Purchase #2	$18.67	12.286%	$20.9638	$20.96	$20.95	$21.00
Purchase #3	$138.70	7.276%	$148.7918	$148.79	$148.80	$148.80
Purchase #4	$249.67	4.670%	$261.3296	$261.33	$261.35	$261.30
Purchase #5	$187.68	11.783%	$209.7943	$209.79	$209.80	$209.80
Purchase #6	$35.74	13.783%	$40.666	$40.67	$40.65	$40.70
Purchase #7	$62.28	4.132%	$64.8534	$64.85	$64.85	$64.90
7 purchase totals =	$731.60		$788.8799	$788.87	$788.90	$789.00