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	$83.65	3.734%	$86.7735	$86.77	$86.75	$86.80
Purchase #2	$173.83	9.868%	$190.9835	$190.98	$191.00	$191.00
Purchase #3	$235.39	9.758%	$258.3594	$258.36	$258.35	$258.40
Purchase #4	$180.25	4.800%	$188.902	$188.90	$188.90	$188.90
Purchase #5	$173.28	13.324%	$196.3678	$196.37	$196.35	$196.40
Purchase #6	$102.75	10.240%	$113.2716	$113.27	$113.25	$113.30
Purchase #7	$135.85	3.693%	$140.8669	$140.87	$140.85	$140.90
7 purchase totals =	$1,085.00		$1,175.5247	$1,175.52	$1,175.45	$1,175.70