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	$6.90	8.209%	$7.4664	$7.47	$7.45	$7.50
Purchase #2	$89.87	7.779%	$96.861	$96.86	$96.85	$96.90
Purchase #3	$28.56	3.256%	$29.4899	$29.49	$29.50	$29.50
Purchase #4	$94.80	10.328%	$104.5909	$104.59	$104.60	$104.60
Purchase #5	$141.46	6.780%	$151.051	$151.05	$151.05	$151.10
Purchase #6	$43.51	9.606%	$47.6896	$47.69	$47.70	$47.70
Purchase #7	$219.73	7.384%	$235.9549	$235.95	$235.95	$236.00
7 purchase totals =	$624.83		$673.1037	$673.10	$673.10	$673.30