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	$88.91	12.815%	$100.3038	$100.30	$100.30	$100.30
Purchase #2	$137.53	6.805%	$146.8889	$146.89	$146.90	$146.90
Purchase #3	$107.79	5.737%	$113.9739	$113.97	$113.95	$114.00
Purchase #4	$49.59	12.825%	$55.9499	$55.95	$55.95	$55.90
Purchase #5	$107.90	9.868%	$118.5476	$118.55	$118.55	$118.50
Purchase #6	$79.86	8.503%	$86.6505	$86.65	$86.65	$86.70
Purchase #7	$189.88	13.848%	$216.1746	$216.17	$216.15	$216.20
7 purchase totals =	$761.46		$838.4892	$838.48	$838.45	$838.50