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	$11.77	4.250%	$12.2702	$12.27	$12.25	$12.30
Purchase #2	$37.52	4.860%	$39.3435	$39.34	$39.35	$39.30
Purchase #3	$208.81	6.698%	$222.7961	$222.80	$222.80	$222.80
Purchase #4	$84.86	5.713%	$89.7081	$89.71	$89.70	$89.70
Purchase #5	$103.34	11.775%	$115.5083	$115.51	$115.50	$115.50
Purchase #6	$7.93	7.611%	$8.5336	$8.53	$8.55	$8.50
Purchase #7	$166.36	3.119%	$171.5488	$171.55	$171.55	$171.50
7 purchase totals =	$620.59		$659.7086	$659.71	$659.70	$659.60