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	$139.38	6.433%	$148.3463	$148.35	$148.35	$148.30
Purchase #2	$94.77	3.785%	$98.357	$98.36	$98.35	$98.40
Purchase #3	$106.88	9.276%	$116.7942	$116.79	$116.80	$116.80
Purchase #4	$145.43	4.167%	$151.4901	$151.49	$151.50	$151.50
Purchase #5	$247.50	6.112%	$262.6272	$262.63	$262.65	$262.60
Purchase #6	$103.48	9.161%	$112.9598	$112.96	$112.95	$113.00
Purchase #7	$84.58	5.628%	$89.3402	$89.34	$89.35	$89.30
7 purchase totals =	$922.02		$979.9148	$979.92	$979.95	$979.90