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	$40.31	7.274%	$43.2421	$43.24	$43.25	$43.20
Purchase #2	$244.25	4.755%	$255.8641	$255.86	$255.85	$255.90
Purchase #3	$211.38	3.499%	$218.7762	$218.78	$218.80	$218.80
Purchase #4	$156.42	12.445%	$175.8865	$175.89	$175.90	$175.90
Purchase #5	$66.62	8.795%	$72.4792	$72.48	$72.50	$72.50
Purchase #6	$169.45	9.213%	$185.0614	$185.06	$185.05	$185.10
Purchase #7	$183.80	5.515%	$193.9366	$193.94	$193.95	$193.90
7 purchase totals =	$1,072.23		$1,145.2461	$1,145.25	$1,145.30	$1,145.30