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	$6.97	5.822%	$7.3758	$7.38	$7.40	$7.40
Purchase #2	$247.73	3.253%	$255.7887	$255.79	$255.80	$255.80
Purchase #3	$71.78	9.320%	$78.4699	$78.47	$78.45	$78.50
Purchase #4	$164.59	5.859%	$174.2333	$174.23	$174.25	$174.20
Purchase #5	$81.89	5.289%	$86.2212	$86.22	$86.20	$86.20
Purchase #6	$41.96	7.566%	$45.1347	$45.13	$45.15	$45.10
Purchase #7	$121.34	9.315%	$132.6428	$132.64	$132.65	$132.60
7 purchase totals =	$736.26		$779.8664	$779.86	$779.90	$779.80